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, core the center of each cupcake. For uniformly-sized holes, you can use the back of a large piping tip to mark the circles. Use a jam knife to cut the hole out.
Fill the hole with a little buttercream. Top with the sprinkles and cover the hole with more buttercream.
Spread a layer of buttercream all over the top of the cupcakes and pipe a large rosette on top of each cupcake.
Sprinkles the tops sparsely with more sprinkles.