Butter or grease a 9x13 pan.
In a large bowl, cream the shortening, butter, and sugar. Beat in the whole egg and the yolks of the other two eggs.
In a separate bowl, stir together the flour, baking powder, and salt.
Combine the flour mixture with the creamed mixture, blending thoroughly.
Spread the batter into the baking pan, patting with your hands if need be.
Sprinkle chocolate chips, marshmallows, and nuts over the batter.
In large bowl, beat the 2 egg whites until stiff. Fold in brown sugar until well combined.
Spread brown sugar meringue over top of marshmallows, spreading to touch the edges of the pan to prevent it from shrinking during baking.
Bake at 350 for 30-40 minutes, or until lightly browned on top. Cool completely and then cut into bars.