Stir cocoa powder into hot butter. (Make sure no drops of water or wet mixing tools are used.) (Assembled ingredients in photo.)
Using electric beaters, beat cream cheese for 1 minute, until lighter in texture.
Add sweetener and cocoa-butter mixture. Beat 1 minute until fluffy.
Use now to frost your cake! Or refrigerate until ready to use; then bring to room temperature. Once your cake is frosted, you can serve it room temperature, but I like it best refrigerated for 1 to 3 hours, or overnight.