Remove breasts from pair of grouse, and sauté in butter. When partially cooked, season with salt and pepper. Break carcasses in pieces, cover with cold water, add carrot, celery, onion, parsley, and bay leaf, and cook until stock is reduced to three-fourths cup. Arrange grouse on a serving dish, and pour around a sauce made of three tablespoons butter, four and one-half tablespoons flour, stock made from grouse, and three-fourths cup stewed and strained tomatoes. Season with salt, cayenne, and lemon juice, and add one teaspoon finely chopped parsley, and one-half cup canned mushrooms cut in slices.