Preheat oven to 350. Cream shortening, butter and sugars. Beat in the whole egg and two egg yolks. Sift flour, baking powder and salt together. Combine the two mixtures and blend thoroughly. Spread batter in greased 9" X 13" pan. Sprinkle nuts, chocolate chips and marshmallows over the batter. Beat the 2 egg whites until stiff. Fold in the brown sugar and spread this on top of the mixture. Bake 35 minutes - you should watch it so your meringue doesn't burn. Cool and cut into bars.
We put these in a covered candy dish for our guests - and they always disappear!!