Allow the butter to come to room temperature. If your coconut oil is not liquid (it turns solid if the temperature is cool) microwave slightly to melt it. Combine the softened butter, coconut oil, cocoa and vanilla in a blender or use a large bowl and a stick blender. When it is combined, pour it into a mini-muffin tin. Freeze for one hour or until the disks are solid. Remove them from the tin and place them into a zip top bag and store in the freezer. Place one disk in the bottom of your coffee cup before pouring in the coffee. Stir vigorously with a spoon or blend quickly with a handheld frothier.