1) In a heavy bottom pan melt butter and add flour to make a roux. Stir constantly over a low heat until it takes on a beige colour and loses the floury taste; about 30 mins. When the roux is done, stir in vegetables, bacon and parsley. Add in beer, clam juice, bay leaf, seasonings and single cream. Stir, and cover pot. Let simmer for 30 to 45 mins. Nearing the end of cooking time, add in precooked crawfish and serve over rice.