Well, when you are drastically carb deprived and craving chocolate, almost anything will do. I’ve had a few of those boxed ones.
There’s one that’s pretty good - has a packet of chocolate that’s kinda like thin fudge to put over it after the cake is done.
If you’re doing Low Carb and crave a chocolate fix, you need to learn about ‘Fat Bombs’ - my husband makes some really good ones.
There are lots of recipes out there.
http://www.wholesomeyum.com/keto-fat-bomb-recipe-chocolate-fat-bombs