Spread on a baking dish a layer of chopped onions cooked until soft in butter mixed with three tablespoons of tomatoes, peeled, pressed and also cooked in butter. Season with a teaspoon of curry. Set a sole on top and pour over it two tablespoons of mushroom stock. Poach in the oven. Set the sole, well drained on the serving dish, the fish having been trimmed and if possible the backbone removed. Add to the cooking liquor 3 tablespoons of Bechamel sauce based on fish stock and three tablespoons of thick fresh cream. Allow to boil for a few moments. Finish off with a teaspoon of butter and a few drops of lemon juice. Coat the fish with this sauce, serve indian style rice separately.