Preheat oven to 350°F. In a mixing bowl, beat egg, Greek yogurt, nut milk, and vanilla extract until combined. Beat in brown sugar and white sugar.
Fold in cocoa powder, all purpose flour, salt, and baking powder. After the batter is thoroughly mixed, fold in chocolate chips.
Pour batter into your well greased skillet. Add graham cracker mixture over top.
Bake for 18-20 minutes or until the middle is cooked. Once the brownie is done cooking, remove from oven, and turn on broiler. Add marshmallows over top.
Add marshmallows on top of your cooked brownie and place on the top rack of the broiler. Broil for 2-4 minutes or until marshmallows are a golden brown.
Enjoy straight from the pan. Use extra graham crackers for scooping.