In a mixing bowl, add the egg whites, corn syrup, and cream of tartar. Mix on high speed until mixture is double in size. I used a KitchenAid, but you can also use a hand mixer.
Reduce the speed to low and add in powdered sugar, vanilla, and cocoa powder until it’s totally incorporated.
Store in the fridge until using.
Notes
I have a few smores tutorials on the blog and I purchased the mold here