Roux for Velouté

• About 1 quart fish fumet
• 2 tablespoons flour
• 1½ tablespoons butter
• 12 grey sole or lemon sole filets
• Salt, pepper
• ½ pound sorrel, parboiled for a few seconds, drained, stewed gently in butter for 15 to 20 minutes, and sieved
• About ⅔ cup heavy cream
• About ¼ cup butter cut into small pieces

Put aside about 1 cup of the fumet in which to poach the filets and, with the rest, prepare the velouté so that it will be ready when the fish is poached: Add the flour to the melted butter in a saucepan and cook gently, stirring, for about a minute without letting it color. Add the fumet slowly (away from the heat if it is hot), stirring all the while, and then cook at a very light boil, the saucepan pulled a bit to the side of the heat, for about ½ hour, skimming (skinning) from time to time.

Soak the filets in cold water for a few minutes, sponge them dry, flatten them slightly with the side of a large knife blade, and, skin side up, slit the thin surface membrane of each, diagonally, at approximately 1-inch intervals. Sprinkle lightly with salt, grind over a bit of pepper, and fold each filet in two, membrane inside (slitting and folding prevent deformation while poaching). Choose a low-sided heavy cooking vessel just large enough to hold the folded filets placed side by side; a copper plat à sauter is perfect, but a cast-iron enamelware frying pan or an earthenware poëlon will do. Arrange the folded filets in the bottom and pour over fumet to barely cover (if the quantity has been underestimated, make up the difference with a bit of white wine; if some fumet is left over, add it to the velouté). Press a buttered round of parchment paper over the surface, cover the pan tightly, and bring to the boiling point, shaking the pan gently from time to time to ensure the liquid’s regular absorption of heat and lifting the lid to check progress. As soon as the boiling point is reached, turn off the heat and leave, tightly covered, to poach for about 8 minutes.

While the filets are poaching you should whisk the sorrel purée into the velouté, adding as much cream as the sauce can support without becoming too thin, and return it to a boil, reducing a bit, if necessary—more cream may be added along with the reduced poaching liquid if the body will then support it.

Drain the poaching liquid into a saucepan, keeping the filets in the pan or transferring them to a heated serving platter. Reduce the liquid over a high flame to a syrupy consistency, add it to the sauce, remove the sauce from the heat, and whisk in the butter. Pour it over the filets (or simply mask them and serve the remaining sauce apart).