Add the butter and vanilla to a large bowl and beat on high until fluffy, about 1 minute. Add the sugar and cocoa. Start out mixing on low speed until all of the sugar is incorporated, 1 to 2 minutes. Increase the speed to high and beat until very light and fluffy, about 2 minutes.

Add the cream, and beat on high for 4 minutes more. Use immediately, or store in a tightly covered container, in a cool dry place, for up to two days. If you choose to refrigerate the frosting, let it come to room temperature before using. Stir vigorously with a butter knife or offset spatula to fluff the frosting back up before using.