Season the crayfish with salt and pepper and set aside. Put the shells and heads in a large frying pan and crush with a pestle. Add the butter and melt over low heat. Add the diced vegetables, thyme, and bay leaf and season with salt and a pinch of cayenne pepper. Cover and cook gently for a few minutes until the vegetables are tender. Add the Cognac and light with a match. When the flames die, add the tomatoes and tomato paste. Stir in the wine and bring to a boil Then lower the heat and simmer, stirring occasionally, until reduced to about 1/2 cup. Strain through a fine strainer, pressing down on the solids with the back of a spoon to extract all the liquid. Discard the residue. Return sauce to the frying pan and whisk in the cream. Reduce over a medium heat until the sauce thickens and coats the back of a spoon. Adjust seasoning.
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18 crayfish, shelled, with shells and heads reserved
