There is no recipe. I just make it up as I go.
Roughly:
Saute green bell pepper, onion and celery in a lot of butter. Sprinkle in some seasoning consisting of salt, paprika, cayenne, pepper, and thyme. Add in crawfish and shrimp. Add in flour to make a paste, then pour in shrimp or crawfish stock. Bring to a boil, then cool. Add in garlic and lemon juice. Maybe a splash of Worcestershire sauce and/or hot sauce. I can't remember if I used them or not. Add chopped parsley when finished and stir.