Preheat oven to 170 °Celsius.
Beat butter and sugar till light and fluffy. Add eggs, one at a time, beating well after each addition.
In a separate bowl, sift flour, salt and baking powder. Fold in the sifted ingredients into the creamed mixture alternately with milk, starting and ending with flour.
Fold in the vanilla extract and give the batter a good mix.
Pour batter into baking cups until they are about two thirds full.
Bake the cupcakes for 15 to 20 minutes (depending on the size of the casing you use) or until a toothpick inserted in the center of the cupcakes comes out without any wet batter sticking to it.
Remove the cupcakes from oven and let them cool completely before decorating.
To decorate the cupcakes, peel them off their casings.
Layer each cupcake into 3.
Mix some sprinkles into buttercream and spread the buttercream onto the first layer of the cupcake. Top with the second layer of cupcake, spread more sprinkles buttercream onto the second layer and top with the final layer of the cupcake.
Lift the layered cupcake into a new cupcake casing.
Pipe simple buttercream swirls on each cupcake and top them with more sprinkles.