In a saucepan, melt butter, blend in flour, onion, salt and pepper. Add milk all at once and cook, stirring constantly until sauce is thickened. Add broccoli and stir on low heat until broccoli is warmed. Stir a little of the hot mixture into beaten eggs, then stir egg mixture into broccoli. Blend well. Turn into a well-greased ring mold or a 1 1/2 qt. Greased casserole dish. Bake at 325 degrees for about 45 minutes, until firm. Insert knife around sides and shake gently to loosen right. Turn onto hot platter. Serve e plain or with cheese or mushroom sauce. Makes 2 to 8 servings.