Soles a la Rochelaise

Remove the black skin from a fine sole; insert the knife on each side to separate the fillets without detaching them; lay the fish on a buttered dish, the black skin side underneath; moisten with white wine and oyster broth, season and set on top some small pieces of butter; place it in the oven to cook without coloring. Drain off the stock, add a minced onion, and reduce it to half, pouring in a little espagnole sauce (No. 414), and thickening with butter and lemon juice; strain this through a tammy; garnish around the sole with mushroom heads and the soft part of oysters; add chopped parsley, pour part of the sauce over the whole, serve the rest separately.