Buttery onion soup

1. In a large kettle, saute onions in margarine over low heat until tender and transparent, about 20-30 minutes.
2. Blend in flour.
3. Gradually add broth and milk; cook and stir over medium heat until bubbly.
4. Cook and stir for 1 minute more; reduce heat to low. Add mozzarella cheese and stir constantly until melted (do not boil).
5. Seasoni to taste with salt and pepper.
6. Serve with croutons if desired.
7. Yield: 6 servings (about 1 ½ qts).
8. A recipe of sharon berthelote of sunburst, montana.