Make the cupcakes:

Preheat the oven to 350°F. Line cupcake tins with wrappers.

In a medium bowl, sift together the flour, baking powder and salt.

In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar until light and fluffy. Add the eggs, one at a time, mixing between each addition then add the vanilla and mix until combined.

Alternately add the flour mixture and milk to the stand mixer in three increments each, beginning and ending with the flour mixture and beating between each addition. Divide the batter into six bowls then dye each with the red, orange, yellow, green, blue and purple food coloring.

Spoon a portion of the purple batter into each cupcake cup, top it with the blue, then green, yellow, orange and red, careful not to mix any of the layers. (Alternately, transfer each color into sealable plastic bags and pipe the batter into the cups.) Bake the cupcakes for 15 to 18 minutes until a toothpick inserted comes out clean. Remove the cupcakes from the oven and transfer them to a rack to cool completely while you make the frosting.

Make the frosting:

In the bowl of a stand mixer fitted with the paddle attachment, cream the butter until it is light and fluffy. Add the vanilla extract and beat until combined then add half of the powdered sugar and continue beating until well combined.

Add the heavy cream and continue beating and then add the remaining powdered sugar and beat until the frosting is thick and creamy. (See Kelly's Notes.)

Once the cupcakes have cooled completely, pipe or spread the frosting onto them then top with rainbow sprinkles and serve.

Kelly's Notes:

Beating the frosting in between each addition of the powdered sugar lightens the color of the frosting and will make it more white in color (rather than yellow).

If the frosting is too thin, add additional sifted powdered sugar 1/4 cup at a time, or if it’s too thick, add additional heavy cream 1 teaspoon at a time until the frosting reaches your desired consistency.