Flour the filet of sole lightly.
Melt butter in a casserole; arrange a layer of sole in casserole.
Dilute cream of mushroom soup with 1/4 can of water, and use 1/2 of this mixture to cover the layer of fish.
Add another layer of sole and cover with the rest of the sauce.
Place in oven (350Â°F) for 30-45 minutes until the sauce is condensed and creamy.