Separate broccoli stalks and cook in 1 inch boiling salted water 3 to 5 minutes. Drain. Arrange broccoli in greased 9-inch square pan. Melt 5 tablespoons butter and blend in flour, salt and pepper. Cook and stir until smooth. Remove from heat and stir in milk. Bring to boil and boil 1 minute, stirring constantly. Add cheese and remove from heat. Saute mushrooms in remaining 1 tablespoon butter until tender and add to sauce. Add green pepper and cook 1 minute. Pour sauce over broccoli. Sprinkle with additional cheese and paprika, if desired. Bake at 350F 15 to 20 minutes.