Melt 1 tablespoon of butter in a saucepan, add just under the same quantity of flour, and stir till quite smooth. Add the hot stock gradually and stir till it begins to thicken. Then add 2 tablespoons of melted butter, stirring continually. Flavour with the essence of mushrooms and the lemon juice, add the cooked and shelled prawns, finely chopped, season with salt and pepper and simmer for 10 minutes. The sauce must be somewhat thick. Remove from the fire and let stand till quite cold.
Bone and fillet the smelts, coat with the sauce, pressing the 2 fillets from each fish together again, so that they look like a whole fish. Roll in flour, coat with the beaten yolks of 1 or 2 eggs, and fry in boiling fat to a golden colour. Drain and put on a hot dish. Green peas, boiled, drained and moistened with a little melted butter, are usually served with this dish.