In the bowl of a stand mixer, combine the butter and powdered sugar and beat until well incorporated, first on low speed, then increase speed to medium-high and mix for three minutes. Scrape down the sides of the bowl then add the vanilla and heavy cream, beating the mixture of an additional three minutes. Add 1 tsp additional heavy cream to reach your desired consistency. Spread or pipe onto your cakes.
This amount will frost a dozen regular size cupcakes, 24 mini cupcakes (like the Better Batter Yellow Cake cupcakes shown in the photo above), or increase the recipe by 50% for a two layer cake (3 sticks of butter, 4 1/2 cups of powdered sugar, etc).