In a medium-sized bowl whisk together the flour, light brown sugar, salt, baking powder, cocoa powder, and chocolate chips
In a separate bowl mix the sour cream, melted butter, and egg. Gently fold the wet ingredients into the dry ingredients. Mix only until just combined. The batter will be thick.
Spoon the batter into the donut pan and place the donut pan on a cookie sheet. Sprinkle the remaining crust mixture on the top of the batter.
Put the donuts into the pre-heated oven and bake for 15-17 minutes or until they spring back when lightly pressed.
Remove from oven allow and allow to cool in the pan for 10 minutes and then remove and allow to cool fully.
Place 4 cut marshmallow pieces on top of each donut. Turn the oven to broil and place back into the oven until the marshmallows are nicely toasted.