Preheat your oven to 350°F. Line a muffin tin with paper liners. In a large mixing bowl, cream together the butter and sugar until light and fluffy. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract. In another bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the butter mixture, alternating with the milk. Fold in the sprinkles.

Fill each cupcake liner about two-thirds full with the batter. Bake for 18-20 minutes or until a toothpick inserted into the center of a cupcake comes out clean. Allow the cupcakes to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.

In a clean mixing bowl, beat the butter until creamy. Gradually add the confectioners' sugar, heavy cream, and vanilla extract, beating on high speed until the frosting is light and fluffy. Adjust the consistency as needed by adding more cream or sugar.

Once the cupcakes are completely cooled, use a spatula or piping bag to apply the buttercream frosting. Decorate with additional sprinkles if desired. Serve immediately for the best taste and texture.

Store any leftover cupcakes in an airtight container at room temperature for up to 3 days. For longer storage, you can refrigerate them for up to a week, but bring them to room temperature before serving for optimal flavor and texture.