Traditional French onion soup can come in as high as 39 grams of fat per serving. Ours has just 10.5 and tastes amazing. Slowly caramelizing the onions gives this soup its diner-divine rich flavor (don’t try to hurry the onions; they’re worth the time!). Slices of toasted sourdough and just enough melted cheese complete the order.
1. Heat butter and oil in heavy, large saucepan over medium heat. Add onions, garlic and salt, and cook 5 minutes, stirring often. Reduce heat to very low, and cook, stirring occasionally, 50 to 60 minutes, until onions are very tender and brown.
2. Stir in flour, and cook 3 to 4 minutes, stirring constantly. Blend in broth, sherry and mustard. Cover, and simmer 15 minutes, stirring occasionally. Stir in sherry vinegar.
3. Preheat broiler. Ladle soup into six heatproof bowls. Top each with slice of toast and grated cheese. Broil until cheese is bubbly and golden, about 1 to 2 minutes. Serve hot.