to serve 6-8
3/4 lb fresh mushrooms
2 ounces butter
2 tablespoons vegetable oil
1/2 ounce finely chopped shallots or spring onion
1-1/4 teaspoons lemon juice
3 lb grey, lemon or petrale sole or flounder fillets, skinned and cut into serving pieces all the same size (I usually use local white fish as sole isn’t readily available)
salt
freshly ground black pepper
12 tablespoons dry white wine
water
Sauce Creme
2 ounces butter
2 ounces flour
5-6 ounces double cream
1 tablespoon lemon juice
1 teaspoon salt
white pepper (I have used black)
2-4 ounces soft butter
Preheat the oven to 350F. Remove the caps from 12 to 16 of the mushrooms and slice the stems and the remaining mushrooms. In a small heavy pan, melt 1 oz of the butter with 1 tablspoon of the oil and lightly brown the whole mushroom caps. Set them aside. In another pan, melt the other 1 oz butter and 1 tablespoon oil, and cook the sliced mushrooms for 2 minutes. Add the shallots and cook another minute. Stir in the lemon juice.
Butter a shallow flameproof serving dish large enough to take the fish in one layer. Lay the fillets in side by side, folding in half if less than 1/4″ thick. Salt and pepper them and spread with the mushroom-shallot mixture. Pour in the wine and enough water to barely come to the top of the fish. Bring to a slow simmer on top of the stove, cover with buttered foil and then cook in the oven 8-10 minutes or until just firm to the touch (I usually leave out the simmer on the stove top bit and put them straight into the oven). Remove from the oven and discard the foil.
Drain all the liquid carefully from the dish (with one of those basting-bulb things if you have one) and strain into a saucepan. Cover the fish and keep it warm. Boil the poaching liquid over a high heat until it reduces to 1 cup.
Sauce Creme:
In a heavy saucepan, melt 2 oz butter over a moderate heat. when the foam subsides, remove from the heat and stir in the flour. Return to low heat and cook, stirring, for a minute or two. Remove from the heat again and slowly pour in the poaching liquid, whisking all the time. Return to high heat and whisk until it boils (it will be quite thick). Whisk in 1/2 a cup of cream and bring back to a simmer, stirring. Thin it gradually with more cream until the sauce coats the spoon with a creamy layer. Season with lemon juice, salt and pepper.
Just before serving, reheat the mushroom caps. Draw off any remaining juices in the fish dish. Remove the sauce from the heat and beat in as much of the soft butter as you like. Spoon the sauce over the fish and garnish with the mushroom caps. Serve at once.