Allow egg yolks and egg whites to stand at room temperature for 30 minutes. Meanwhile, in a medium saucepan cook celery, green onion, and garlic in butter or margarine about 5 minutes or until tender. Stir in flour, mustard, salt, and pepper. Stir in milk all at once. Cook and stir until thickened and bubbly. Reduce heat; add Camembert and Parmesan or Romano cheeses, a little at a time, stirring until melted. Remove from heat; set aside.
In a medium mixing bowl beat egg yolks with an electric mixer on high speed for 5 minutes or until thick and lemon colored. Gradually beat in cheese mixture. Wash beaters with warm, soapy water; dry beaters. In a large mixing bowl beat egg whites until stiff peaks form (tips stand straight). Gently fold 1 cup of the stiffly beaten egg whites into egg yolk-cheese mixture. Gradually pour over remaining egg whites, folding to combine. Turn into an ungreased 2- to 2-1/2-quart souffle dish. Bake in a 350 degree F oven about 40 minutes or until a knife inserted near center comes out clean. Serve immediately. Makes 6 servings.