Preheat the oven to 350 degrees. Line a standard muffin tin with cupcake liners and set aside.

In the bowl of a stand mixer, combine the sugar and softened butter. Cream until smooth.

Add in the eggs, milk and vanilla. Mix until combined, scraping down the sides often.

Add in the remaining dry ingredients - flour, baking powder, and salt. Mix well, scraping the sides as needed.

Fold in the sprinkles.

Divide the batter between each of the cupcake liners, filling about ½-⅔ full.

Bake in the preheated oven for 14-16 minutes or just until starting to golden and center is set. Allow to cool completely before decorating.

In the bowl of a stand mixer, combine the softened butter, vanilla, salt and about half of the powdered sugar.

Mix on low until combined.

Add in the remaining powdered sugar and the milk and mix on low until combined.

Bump up the speed to medium and whip for about another minute or until light and fluffy.

Transfer the frosting to a piping bag fitted with a large star tip.

Once cupcakes are cool, pipe a mound of frosting on each cupcake and sprinkle with additional rainbow sprinkles to decorate.