Preheat an oven to 350 degrees F. Line a muffin tin with cupcake liners.
In a large mixing bowl, use a hand mixer to cream the butter and sugar together. Beat in vanilla extract.
Beat in eggs, buttermilk, baking powder, and salt until smooth. Slowly add in flour until just combined.
Gently stir in sprinkles using a rubber spatula. Do not over stir or colors will bleed.
Fill each cupcake liner 1/2 full. Bake in the 350 degree oven for 15 to 18 minutes until a toothpick inserted into the center comes out clean.
Remove cupcakes from tin and transfer to a wire rack to cool completely.
To make frosting, beat softened butter with vanilla extract and 2 cups powdered sugar until light and fluffy. Slowly add in remainder of powdered sugar and use milk to thin as needed. Transfer to a piping bag to frost. Decorate with additional sprinkles.