Slow-Cooked French Onion Soup Recipe
Deeply caramelized onion soup topped with crusty bread and melted Gruyère
By Sarah Mitchell • June 14, 2026
French onion soup is all about patience. Slowly caramelizing onions for 45 minutes transforms them from sharp and pungent to sweet, jammy, and deeply flavored.
The broth is rich beef stock deglazed with a splash of cognac or dry sherry. Ladle into oven-safe bowls, top with thick slices of crusty bread and a generous layer of Gruyère, then broil until bubbly and golden.
Don't rush the onions — low and slow is the only way.
About This Recipe
"Slow-Cooked French Onion Soup" is a Soups & Stews recipe that brings yellow onions, thinly sliced, butter, olive oil, beef broth and dry sherry or white wine together into a flavorful, well-balanced dish. Rated Medium and ready in about 75 minutes, this recipe fits easily into a busy schedule. It serves 6 and works equally well for a weeknight dinner or a relaxed weekend meal. The French inspiration behind this dish balances classic techniques with clean, vibrant flavors.
Ingredients
- 5 large yellow onions, thinly sliced
- 3 tbsp butter
- 1 tbsp olive oil
- 6 cups beef broth
- 1/2 cup dry sherry or white wine
- 1 tsp fresh thyme
- 6 thick slices French bread
- 2 cups shredded Gruyère cheese
- 1 tsp salt
Instructions
- 1
Cook onions in butter and oil over medium-low heat for 40-45 minutes, stirring occasionally, until deeply caramelized.
- 2
Add sherry and scrape up the fond. Cook 2 minutes.
- 3
Add beef broth and thyme. Simmer 15 minutes. Season with salt and pepper.
- 4
Ladle into oven-safe bowls. Float bread on top. Cover with Gruyère.
- 5
Broil 3-4 minutes until cheese is bubbly and golden. Serve immediately.
Expert Tips
For the best result, use the freshest, highest-quality ingredients you can find. Yellow onions, thinly sliced is the heart of this dish, so choose it with care. Read the recipe through before you start and prep all ingredients in advance (mise en place) so the cooking process is smooth. Oven and stovetop work especially well for this preparation. Taste and adjust salt, pepper, and acid at the end to make the flavors pop.
What To Serve With This
"Slow-Cooked French Onion Soup" is a versatile Soups & Stews dish that pairs beautifully with a simple side salad, buttered green beans, roasted potatoes and classic French sides. Choose at least one fresh and one hearty side to create a balanced meal.
Storage & Reheating
Slow-Cooked French Onion Soup stores well in an airtight container in the refrigerator for 2–3 days. Let it cool to room temperature before refrigerating before sealing the container. Reheat gently until warmed through, adding a small splash of liquid if needed to restore the original texture.
Nutrition Facts (per serving)
Frequently Asked Questions
How long does it take to make Slow-Cooked French Onion Soup?
This recipe takes about 15 minutes of prep and 60 minutes of cooking, for a total of roughly 75 minutes. It serves 6 and is rated Medium.
How do I store leftover Slow-Cooked French Onion Soup?
Store leftover Slow-Cooked French Onion Soup in an airtight container in the refrigerator for up to 3-4 days. Make sure to let it cool to room temperature before refrigerating. Reheat in the oven or on the stovetop for best results.
Can I make Slow-Cooked French Onion Soup ahead of time?
Yes, you can prepare Slow-Cooked French Onion Soup in advance. Store it in an airtight container in the refrigerator for up to 3 days. Reheat gently before serving to preserve the best texture and flavor.
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