1 onion, minced
6 tbsp. butter, divided
4 tbsp. all-purpose flour
2 cups milk
1/2 tsp. salt
1/8 tsp. pepper
1 egg yolk
1 cup grated Parmesan cheese
2 1/2 lb. broccoli, steamed
1/2 cup dry bread crumbs

Cook onion in 4 tablespoons butter until tender. Stir in flour. Add milk gradually and cook slowly until thick, stirring constantly. Add salt, pepper, egg yolk and cheese. Pour half the sauce into greased baking dish. Arrange broccoli on top of sauce. Cover with remaining sauce. Sprinkle with bread crumbs and dot with remaining 2 tablespoons butter. Bake in hot (400°F) about 20 minutes uncovered.