Using an electric mixer, on medium speed, cream the butter until smooth. With the mixer in the o position, add the cocoa powder and ó of the powdered sugar to the bowl. Mix on low speed until combined. Beat in the vanilla, Coca-Cola®, and as much additional powdered sugar as needed to achieve desired consistency. Beat on medium speed for an additional 1 to 2 minutes, or until the frosting is completely smooth.
To assemble: Spread or pipe desired amount of frosting on each cupcake. Serve.
