Line bottom of soufflé dish with slices of bread or use deep casserole dish.
In pan mix oil and flour. Heat slowly. Stir in milk until thickened. Add salt, mustard and pepper.
Remove sauce from heat. Add grated cheese. Stir until melted. Cool. Add chopped broccoli and let cool.
Add egg yolks one by one to broccoli mixture. Let mixture stand while you beat the egg whites until they hold firm peaks. Take a large spoon and gently fold in all of egg whites.
Turn into soufflé or casserole dish. Bake at 350° F for 50 to 55 minutes. Do not open oven while soufflé is baking.
Makes: 4