Preheat oven to 350 F. Grease and flour 9x13 inch baking pan.
In a medium mixing bowl, beat egg whites to stiff peaks. Set aside.
In a large mixing bowl, cream together butter and sugar until light and fluffy. Stir in egg yolks, baking powder and flour. Add milk and vanilla, and stir to combine. Add graham cracker crumbs, and stir until thoroughly combined. Add 1/3 of the stiff egg whites, and fold until combined. Add half of remaining egg whites and fold in. Add remaining egg whites and fold in until just combined.
Spread batter evenly in prepared baking pan. Bake in preheated oven 15 to 20 minutes until toothpick inserted near the center comes out clean. Note:Watch the cake closely in the last minutes of baking to prevent overcooking.
Sprinkle marshmallows over the top of the warm cake. Turn off the oven and let cake sit 4 to 6 minutes in hot oven to soften. Remove from oven and let cool in pan on wire cooling rack.
In microware, melt chocolate chips, stir until smooth. Drizzle melted chocolate over marshmallow topped cake. Let cool completely. Makes 16 servings.