Heat the oven to 325°F and pan spray an 8×8” baking dish.
In a large microwave safe bowl, melt the butter and ½ cup chocolate chips together in 30 second spurts until smooth and combined.
Stir in the sugar until well combined, then the eggs and vanilla until smooth. Stir in the flour, cocoa powder, malted milk powder, salt and baking powder, mixing until smooth and combined.
Pour and spread the brownie cake batter evenly across the greased pan’s perimeter, scatter mini marshmallows and ⅓ cup chocolate chips atop and bake at 325°F for 35-40 minutes.
Cool completely at room temperature before cutting into nine 2 ½” squares.
