Brown onions to a light golden color in butter in a saucepan. Clean
leeks well and slice.Peel potatoes and slice. Add leeks, potatoes,
ham bone, thyme and stock (or water) to onion. Cover and simmer until
potatoes are very soft.Remove ham bone, discard. Cool potato/leek
mixture slightly. Puree in a food processor or blender and return to
pot. Add cream and cook a few minutes longer.Season with salt and
pepper to taste. Serve with croutons. Makes about 6 servings.