Place the crawfish tails in a bowl and blend in some Creole seasoning. Set aside.
Chop the shallots and garlic very fine and set in separate prep bowls.
Finely chop the green onions and roughly chop the parsley and set aside in separate bowls.
Measure the butter, flour, creole seasonings, Worchestershire sauce and sherry. Pour the heavy cream in a measuring cup and let it come to room temperature.
To make the sauce
Melt the margarine in a large saute pan over medium heat.
When margarine is bubbling, add the shallots and saute for about 3 minutes until softened.
Add garlic, Creole seasonings and kosher salt and pepper, stir for about 2 minutes. [Note: if your Creole Seasoning contains salt, taste before adding any more salt]
Increase heat to medium-high; add the parsley, crawfish tails, and AP flour. Stir to combine all ingredients thoroughly. See Notes.
Saute for about 3 minutes, stirring constantly.
Next add the Worcestershire sauce, sherry and green onions to the pan and stir constantly for about 1 minute.
Increase the heat; add the heavy cream and stir or whisk until thoroughly combined.
Don't let the sauce come to a complete boil. As soon as you see a simmer starting around the edges, lower the heat to maintain a low simmer. (see Notes)
Simmer for about 10 to 15 minutes, stirring and shaking the pan often until thickened slightly.
This recipe was developed using Le Bon Papa Creole Seasoning which is salt-free. Be sure to taste the recipe before adding additional salt if the CReole Seasoning you use is not salt-free. This is a cream sauce so don't start with a roux. Add the flour later in the process (with the crawfish tails) and it will serve to thicken the sauce along with the heavy cream.Using margarine instead of butter will help the sauce stay together and not separate. If the sauce does begin to separate, simply whisk the warm sauce until it's back together.Try not to let the sauce come to a heavy boil after adding the cream. This may cause the sauce to separate and curdle.You can substitute any dry white wine or this or even a light rum for the sherry. Of course, you could leave it out altogether.This sauce is great spooned over fried or broiled fish, stuffed peppers, and pasta. There really is no end to how you will use this sauce.