In large saucepan, melt butter over medium heat. Add chopped onion and cook until tender. Add flour and mix well. Slowly pour in chicken broth and evaporated milk, stirring constantly.
Hollow out one baked potato and reserve skin. Mash. Add to saucepan. Chop remaining potatoes into large chunks and add to saucepan. Cut up potato skin and add to mixture also, stirring after each addition. Cook over medium heat until heated through. Be careful not to scorch.