Crab Meat Au Gratin

INGREDIENTS

• 1 lb crabmeat, white (from body)
• 3 tablespoons butter
• 1/2 cup onion, finely chopped (or scallions)
• 1/4 cup celery, finely chopped
• 1 tablespoon all-purpose flour
• 1 1/2 cups milk
• 1 egg yolk, well beaten
• 2 tablespoons fresh lemon juice
• 1/2 teaspoon prepared mustard
• 3/4 cup grated American cheese (or Cheddar)
• 1 pinch ground nutmeg
• 3 tablespoons breadcrumbs
• 1 dash white pepper
• 1/4 cup cheddar cheese, extra for topping
• 1 dash cayenne pepper
• 1 dash paprika