Preheat oven to 350 degrees. Beat together the granulated sugar and butter until creamy. Beat in 1 whole egg and 2 egg yolks (put aside the whites for later).
In a separate bowl, mix together the flour, salt and baking powder. Add to the butter mixture and mix well. Spread into 9 x 13" pan. Sprinkle with marshmallows and chocolate chips. Beat egg whites until stiff peaks form. Fold in the brown sugar.
Spread the meringue mixture over the marshmallows and chocolate chips. Bake in a preheated 350 degree oven for about 30 minutes or until bars are a deep golden brown and the crust is cooked through. You may have to cook them a bit longer than 30 minutes to get the bottom crust completely cooked through. Cool in pan and cut. If the meringues starts to browns to quickly cover lightly with a piece of foil sprayed with baking spray.