Melt butter in a large, heavy saucepan over medium heat. Add onion and next 7 ingredients; sauté 5 to 7 minutes or until vegetables are tender.
Add flour and cook, stirring constantly, 10 minutes or until mixture is a rich, dark brown.
Stir in stock, and simmer over medium-low heat 45 minutes. Add crawfish, and cook until heated. Stir in sherry, green onions, and parsley. Add Creole seasoning to taste.
Serve over hot cooked rice with hot sauce on the side.