This recipe makes enough mascarpone frosting for a sheet cake, large round cake, or 12 cupcakes. If you want to make a layer cake, multiply the recipe by 1 ½ or even 2 to make sure you have enough for all the layers.
This frosting needs to be used immediately to frost cake so make sure your cake is ready to be frosted.
Using a mixer fitted with the whisk attachment, whisk mascarpone cheese, cocoa powder and powdered sugar on medium speed until combined. Stop occasionally and scrape down the sides and bottom of the bowl with a rubber spatula. Because the cheese is cold it’s ok if it takes 1-2 minutes or more until it’s combined (If it doesn't come together easily, you can use the paddle attachment, and switch to the whisk attachment before adding the heavy cream). Add heavy cream and gradually increase speed to high. Whisk until desired consistency is reached; for a frosting that holds its shape well whisk until stiff peaks - keep whisking until the peaks stand straight up and appear firm when beaters are lifted up. Be careful at that point not to overwhip, which will cause the cream to have a grainy texture or eventually turn into butter. Use immediately.