Cook sprouts, drain, and chop. Melt butter and add flour, salt, and pepper. Add milk and onion and stir until thickened. Beat egg yolks and add to warm sauce. Add cheese and cook for one minute, stirring constantly. Add sprouts and remove from heat. Beat egg whites until stiff and fold into hot mixture. Turn into ungreased 2 litre souffle dish. Bake at 300� for 1.5 hours and serve immediately.
Serves: 4 to 6