Put eggs in bowl. Season with salt and pepper. Beat with rotary beater, only until eggs are slightly frothy.
Heat small amount of oil in pan. Gently sauté finely chopped mushrooms one minute. Remove from pan, drain, add to beaten eggs. Add finely chopped shallots, finely chopped celery, shelled prawns and well-drained bean sprouts. Mix Well.
Add enough oil to medium-sized frypan just to cover base when oil is hot, pour omelet mixture into pan using cup to make four small omelets.
When mixture is firm on one side, separate omelets with spatula. Turn, cook other side. Stack on Warm plate while cooking other omelets. To serve stack omelets on top of each other spoon over sauce.
Sauce: Blend water and cornflour until smooth, add crumbled stock cubes, sugar, soy sauce and salt. Stir until sauce boils and thickens.