My kids don't like, in fact hate dark chocolate because of the bitter after taste. That is why I added the white chocolate to balance the taste. Add in milk or unsweetened chips as per your taste.
For the flax egg, combine 1 tbsp milled flax seeds with 3 tbsp water and set aside till it turns glutenous. I made this first in the mixing bowl, the mixture would look gloopy. Then added the yogurt and went ahead.
In case you don't have flaxseeds, just replace it with an extra 1/4 cup yogurt.