1. Preheat oven to 350. 2. Grease 1-1/2 quart casserole. 3. Thinly slice onions and dice celery. 4. In 3 quart saucepan over medium heat melt butter then cook green onions and celery until tender stirring occasionally. 5. Stir in flour and pepper and cook 1 minute. 6. Gradually stir in milk and cook stirring constantly until mixture boils and thickens then stir in lemon juice. 7. In small bowl with a fork beat egg yolk then beat in small amount of hot sauce. 8. Slowly pour egg mixture back into sauce stirring rapidly to prevent lumping. 9. Reserve 1/4 cup cheese for topping. 10. Stir remaining cheese into sauce until cheese melts and mixture is smooth. 11. Stir in crabmeat then spoon mixture into casserole. 12. Slice tomatoes 1/4 inch thick and arrange over top of casserole. 13. Sprinkle with bread crumbs and reserved cheese. 14. Bake uncovered for 20 minutes.
