Quick Potato Soup

• ¼ pound good butter
• 4 large potatoes
• 4 large onions

Melt the butter in large kettle, or in fireproof casserole in which the soup can be served. Grate the clean potatoes into it. (I like to leave them unpeeled, but the soup is not so pretty unless chopped fresh herbs, added at the last, change its natural whiteness enough to hide the bits of brown skin ...) Grate the peeled onions into it... or slice them very thin. Heat the mixture to bubble-poi