Preheat oven to 160 °Celsius. Prepare two 7 inches round baking trays (greased and floured).
Sieve flour, baking powder and salt and keep it aside.
In a clean bowl, cream the butter, and castor sugar until light and fluffy. Add the egg and continue beating until it is well incorporated and the mixture is all light and creamy.
Fold in the flour alternately with milk, starting and end with flour.
Finally, add the vanilla extract and mix well.
Pour cake batter into prepared tins and bake for about 40 to 45 minutes until the center of the cake springs back when pressed lightly. You can also use a toothpick to test if the cake is done. The toothpick should come out clean when inserted in the center of the cake.
Remove cakes from oven and let them rest in the tins for a few minutes before turning them over onto wire racks to cool completely.
To make the buttercream, add butter into a medium bowl. Cream it until soft.
Sift in the powdered sugar. Beat again until the mixture turns light and fluffy. Add the vanilla extract and mix until well combined.
If the icing appears too stiff, add some milk or cream. Start with small quantities of half or one teaspoon to avoid too much liquid in the buttercream.
To assemble the cake, level each cake layer into 2 and level the tops.
Apply buttercream frosting between each cake layer and stack the layers up.
Once the layers are stacked, give the whole cake a thin crumb coat. Place the crumb-coat frosted cake in the fridge for about 20 minutes for the buttercream crumb coat to set.
Remove from the fridge and apply the final layer of the vanilla frosting with your palette knife. Start with the top of the cake and move to the sides. For this design, it is not necessary to smooth frost the cake, so it is generally a very simple and quick buttercream cake decorating idea. Nevertheless, eyeball to make sure the icing is evenly applied and there are no parts of the cake that look bulging with icing.
To complete the moist vanilla cake decoration, randomly pipe some simple rosettes in Wilton Burgundy and Rose Petal pink using star piping tip 21. For the leaves, tint some buttercream with Wilton Juniper Green and pipe with leaf tip 352. To complete the decoration, pipe a pearl border using round tip 12.