Using challah dough:
Chocolate babke filling is pretty much 1:1:1 ratio of dutch cocoa, sugar and confectioner's sugar. (For one babka, about 1/2 cup of each). Plus good semisweet chocolate chips or baking choc. - if you are using 1/2 measure, then use 1/4-1/3 cup chocolate chips. Mix all of those dry ingredients together.
Roll out the dough, spread a thin layer of oil to cover the entire rolled out dough, then sprinkle dry mixture over in an even layer. Roll up lengthwise, fold roll in half & twist. Place in challah/loaf pan, brush with egg and sprinkle with a simple streusel topping (flour, sugar, margarine/butter).
For the streusel:
½ cup all-purpose flour
¼ cup brown sugar, packed
½ stick unsalted butter
½ tsp ground cinnamon