The onion is prized today in kitchens around the world, particularly in onion soup. It is the best of soups for cold weather. In France onion soup may be made with stock or with water; it may be enriched with dry white wine or a bit of dry red wine.
Melt half of the butter in a saucepan. Cook the onions in it until they are transparent and golden. Add the flour and stir. Cook for three minutes longer. Add the stock and simmer for at least thirty minutes. Add salt and pepper to taste.
Toast the bread slices and butter the toast with the remaining butter.
Preheat oven to moderate (375°F.).
Pour the soup into a large earthenware casserole. Add the wine and half of the grated cheese. Cover the surface with the pieces of buttered toast. Sprinkle all with the remaining grated cheese and add the slices of cheese. The object is to cover the liquid completely with toast and cheese.
Place the casserole, uncovered, in the oven for about fifteen minutes, until the cheese and bread are brown and crusty.