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    Decorated Treats » Recipes » Designs & Tutorials

    Little Mermaid Birthday Cake

    Published: Sep 19, 2020 · Modified: Aug 5, 2022 by Priya Maha

    Jump to Recipe

    If your child is a Little Mermaid fan, you will love this Little Mermaid birthday cake. Baked into a rectangle cake and covered in buttercream, the cake is topped with a toy Little Mermaid figure and handmade fondant Sebastian and octopus. It is easy to put together and real fun too!

    Poster for Ariel Little Mermaid Birthday Cake.

    I made this Ariel Little Mermaid birthday cake back in 2012. It was for a 4-year-old girl. The mom had also separately ordered a castle cake for the school celebration (click here to see how I made the castle cake). This Disney Little Mermaid birthday cake was meant for celebration at home with family.

    The buttercream birthday cake was fairly easy to decorate. Ariel on the cake was a toy figurine. And the only other 3D fondant decoration on the cake were Sebastian and an octopus. The cake itself was covered in butter icing and accented with fondant decorations.

    If you like this cake, you should also check out this other Ariel Little Mermaid cake design. And for more princess themed cakes, check out this Belle cake, Olaf cake and cupcakes and this buttercream castle cake with Princess toppers.

    Jump to:
    • 🧾Supplies Required
    • 👩‍🍳How to Make
    • ❤️More Cake Designs You Will Love
    • 📖Recipe

    🧾Supplies Required

    • Cake - this was a one layer birthday cake, baked in 6 inches by 10 inches rectangle cake pan. I used half the measurement of my pound cake recipe calculated for an eight-inch square cake.
    • Butter icing - Since the cake was only one layer (with a height of about 2 inches), I did not layer and fill it further. I only covered the cake with butter icing. This icing is a much stiffer version of buttercream.
    • Fondant - I used this for the accents as well as to make the sea animals - Sebastian and the octopus. I used my homemade recipe and you can find it here.
    • Food color - I used Wilton gel colors in red, yellow, green, black, and violet.
    • Star cutters - I used star-shaped cutouts on the cake board to place the birthday girl's name.
    • Alphabet cutters.
    • Ariel Little Mermaid cake topper - This was provided by the customer. She preferred a toy topper instead of an edible one so that her daughter could keep it and play with it later.
    • Brown sugar - I used brown sugar to decorate the cake board, to give it a sandy beach feel.
    • Pizza cutting wheel.

    👩‍🍳How to Make

    Step 1: Make Fondant Sebastian and the Octopus Toppers

    I prepared Sebastian and the octopus toppers for the Little Mermaid cake ahead of time. And made them both out of my homemade fondant which dries hard. Hence, there was no need to add any tylose or CMC to it.

    But if you use store-bought fondant, it is best to add tylose or CMC to it before shaping into these toppers.

    Sebastian cake topper made of fondant, on a buttercream covered cake.
    Sebastian cake topper made of fondant, on a buttercream covered cake.
    Fondant octopus in yellow, holding a number 4.
    Top view of a yellow fondant octopus on a buttercream cake.

    Step 2: Bake the Cake and Cover with Butter Icing

    Next was the Little Mermaid birthday cake. I baked a single layer cake (hence it is not filled with any buttercream) and covered it with icing. As I mentioned earlier, butter icing is a much stiffer version of buttercream. It is stiff enough that you can take it with hand without it sticking all over.

    And because of this stiff consistency, piping this icing with a piping bag is not very easy. What I did was take a little of the icing at a time in my hands and flatten it directly onto the cake. I purposely left the finishing rough so that it looked like sea waves on the cake.

    To make the waves, all I did was use my fingertips to press on the icing and make the dents on the cake).

    A Little Mermaid sheet cake decorated in buttercream and toy Ariel topper. On Ariel sides are fondant Sebastian and a yellow octopus.

    Step 3: Assemble the Birthday Cake

    I used a large square cake board for this Little Mermaid birthday cake. I purposely placed the cake on one side of the board. This is so that there is ample space at the front for me to place the birthday girl's name.

    Next, I made the fondant stones for the Ariel cake topper to sit on. To make the stones, I added some black coloring into white fondant. For the marbled effect, I kneaded it by twisting both colors until the white and black were only just mixed. I then formed rough balls and stacked them on one another.

    And then I placed Ariel Little Mermaid figurine on the stones while they were still soft. This is so that the stones could be adjusted to hold the Little Mermaid in place.

    Ariel the Little Mermaid cake topper on a fondant stone on a cake.

    Step 4: Add the Decoration to the Sides of the Cake

    For the sides of the Little Mermaid birthday cake, I used Wilton Pattern Press Set to imprint scrolls all around the cake.

    And then, I cut seagrass out of fondant. I cut these freehand using my pizza cutter. And attached them randomly to the sides of the cake as well as the stones earlier. Since the cake was covered in butter icing, the grease was enough to hold the grass in place. No glue was required. The fondant had no trouble sticking to the icing. 

    Sides of a buttercream covered cake decorated with fondant grass.

    Step 5: Attach the Lettering

    Once the main decorations on the Little Mermaid birthday cake was done, I placed Sebastian cake topper and the octopus cake topper on the cake. And then I sprinkled brown sugar on the cake board.

    Next, I did the lettering on the cake. The words "Happy Birthday" were cut out of fondant. I placed them on the cake itself. The birthday girl's name was placed on star cutouts, on the cake board.

    And I cut out a 3D number "4" for the girl's age, poked a toothpick to it and inserted it near one of the octopus's tentacles, as if the octopus was holding it. 

    Fondant letters on star cutouts on a cake board.

    Letters cut out of fondant for the Little Mermaid birthday cake

    Fondant letters on star cutouts on a cake board.

    Letters cut out of fondant for the Little Mermaid birthday cake

    And that was it! An easy to make Little Mermaid birthday cake.

    A Little Mermaid sheet cake decorated in buttercream and toy Ariel topper. On Ariel sides are fondant Sebastian and a yellow octopus.

    ❤️More Cake Designs You Will Love

    • A two layered butterfly pea cake frosted with white cream cheese frosting and decorated with blue fondant flowers and blueberries on a white cake stand, with a section cut out.
      Butterfly Pea Cake with Lemon Cream Cheese Frosting
    • A round rosette cake in white, pink, burgundy and green.
      Rosette Cake (Buttercream Cake Recipe)
    • A round black cake with Star Wars themed cake.
      Star Wars Birthday Cake (How to Make)
    • A round double barrel cake decorated with Simba cake topper, Lion King edible image and green fondant palm leaves.
      Lion King Cake with Simba Cake Topper

    Do you like this tutorial? Please leave a 5-star ⭐⭐⭐⭐⭐rating in the recipe card below and consider a review further down this page. I would love to hear from you. Thank you!

    📖Recipe

    A Little Mermaid sheet cake decorated in buttercream and toy Ariel topper. On Ariel sides are fondant Sebastian and a yellow octopus.

    Little Mermaid Birthday Cake

    This Disney the Little Mermaid birthday cake is a one layer sheet cake decorated in butter icing and fondant toppers. Get the tutorial here!
    5 from 1 vote
    Print Pin Rate
    Course: Dessert
    Cuisine: American
    Prep Time: 25 minutes minutes
    Cook Time: 50 minutes minutes
    Decorating time: 3 hours hours
    Total Time: 4 hours hours 15 minutes minutes
    Yield: 1 six inches by 10 inches rectangle cake
    Author: Priya Maha
    Prevent your screen from going dark

    Equipment

    • Star cutters
    • Alphabet cutters
    • Ariel Little Mermaid cake topper
    • Pizza cutting wheel
    Metric - US Customary

    For best results, use the metrics measurements. US customary measurements have not been tested and are only meant for guide.

    Ingredients

    Cake

    • 300 g butter
    • 300 g granulated sugar
    • 300 g self-raising flour
    • 5 eggs
    • 75 ml milk
    • ¼ teaspoon salt
    • ½ teaspoon baking powder
    • 1 teaspoon vanilla extract

    Frosting and decoration

    • Butter icing
    • Fondant
    • Brown Sugar
    • Food color in red yellow, green, black, and violet.
    Metric - US Customary

    Instructions

    Baking the cake

    • Preheat oven to 170 °Celsius.
    • Beat butter and sugar till soft and creamy for about 2 minutes. Add eggs, one at a time, beating well after each addition.
    • In a separate bowl, sift flour, baking powder, and salt. Fold in the sifted ingredients into the creamed mixture alternately with milk, starting and ending with flour.
    • Finally, add in vanilla extract and combine well. Pour batter into a well greased and floured cake pan and bake for 45 to 50 minutes until the top of the cake springs back when lightly pressed. The cake is done when a skewer inserted in the center of the cake comes out without any wet batter.
    • Remove the cake from oven and let it cool completely before icing and decorating.

    Sebastian cake topper and the Octopus cake topper

    • Prepare the Sebastian and the octopus toppers for the Little Mermaid cake ahead of time. Make them both out of fondant. Add some CMC powder to the fondant before shaping these toppers to help them set firm.

    Preparing the cake

    • Once the cake has completely cooled down, level the top and crumb coat it. This is a single layer cake, hence there is no need to fill it with buttercream.
    • Cover the cake with blue tinted butter icing. Butter icing is a much stiffer version of buttercream. It is stiff enough that you can take it with hand without it sticking all over.
    • And because of this stiff consistency, piping this icing with a piping bag is not very easy. To cover the cake with butter icing, simply take a little of the icing at a time in your fingers and flatten it directly onto the cake. In doing this, you need not smooth the icing so much. Leave the finishing rough so that the icing looks like sea waves on the cake.
    • To make the waves, all you need to do is use your fingertips to press on the icing and make the dents on it.

    Assembling the Ariel Little Mermaid birthday cake

    • Place the cake on a large square cake board, making sure there is ample space on the front of the cake board to place the birthday girl's name.
    • Next, make the fondant stones for the Ariel cake topper to sit on. To make the stones, add some black coloring into white fondant. For the marbled effect, knead it by twisting both colors until the white and black are only just mixed.
    • Form rough balls and stack them on one another. And then place Ariel Little Mermaid figurine on the stones while they are still soft. This is so that the stones could be adjusted to hold the Little Mermaid in place.
    • Next, place Sebastian cake topper and the octopus cake topper on the cake. And then sprinkle brown sugar on the cake board.

    The decoration on the sides of the sheet cake

    • For the sides of the Little Mermaid birthday cake, you can use Wilton Pattern Press Set to imprint scrolls all around the cake.
    • And then, cut the seagrass out of fondant. You can cut these freehand using a pizza cutter. And attach them randomly to the sides of the cake as well as the stones earlier. Since the cake is covered in butter icing, the grease would be enough to hold the grass in place. No glue is required.

    Lettering on the cake

    • Cut the words "Happy Birthday" out of fondant. Place them on the cake itself. The birthday girl's name is placed on star cutouts, on the cake board.
    • Next, cut out a 3D number "4" for the girl's age, poke a toothpick to it and insert it near one of the octopus's tentacles, as if the octopus is holding it to complete the cake decoration.

    Nutrition

    Calories: 4762.6kcal | Carbohydrates: 522.8g | Protein: 68.8g | Fat: 272.6g | Saturated Fat: 163.3g | Polyunsaturated Fat: 15.6g | Monounsaturated Fat: 72g | Trans Fat: 9.9g | Cholesterol: 1472.7mg | Sodium: 3073.5mg | Potassium: 804.1mg | Fiber: 7.2g | Sugar: 305.6g | Vitamin A: 8816.3IU | Calcium: 456.7mg | Iron: 7mg
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    A Little Mermaid sheet cake decorated in buttercream and toy Ariel topper. On Ariel sides are fondant Sebastian and a yellow octopus.

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