French Onion Soup Recipe

Prepare onions

Peel and thinly slice onions into half-moons about 1/8–1/4" thick. Measure slices; you should have roughly 6 cups.

Caramelize onions

In a large heavy-bottomed pot (6–8 qt) set over medium heat, melt 3 tbs unsalted butter with 1 tbs olive oil. Add the sliced onions, 1 tsp salt, 1 tsp sugar, and 1 tsp freshly ground black pepper. Stir to coat. Reduce heat to medium-low and cook, stirring every 3–5 minutes, scraping browned bits from the bottom. Continue for 35–45 minutes until onions are a deep golden brown and very soft. If the onions begin to stick or brown too quickly, lower the heat; if they dry out, add 1–2 tbs water to deglaze.

Build roux and deglaze

When onions are deeply caramelized, push them to the side and sprinkle 2 tbs all-purpose flour over the onions. Stir to combine and cook for 1–2 minutes to remove raw flour taste. Pour in 1 cup dry red wine to deglaze, scraping up the fond from the bottom of the pot. Let the wine reduce by about half, 3–5 minutes.

Add broths and aromatics

Add 8 cups beef broth and 1 cup beef consommé (or an additional cup of beef broth if not using consommé). Add 3 thyme sprigs, 2 bay leaves, 1 tbs Worcestershire sauce, and 2 tbs sherry or cognac if using. Stir, raise heat to bring to a gentle simmer, then reduce heat and simmer uncovered for 20–25 minutes to meld flavors. Taste and adjust seasoning with additional salt and pepper as needed. Remove thyme sprigs and bay leaves before serving.

Prepare baguette toasts

Preheat oven to 400°F (200°C). Slice the baguette on the diagonal into 1/2"–3/4" thick slices (about 12–14 slices). Brush both sides lightly with 2 tbs olive oil or melted butter. Arrange on a baking sheet in a single layer and bake 8–10 minutes, flipping once, until golden and crisp. Remove and let cool slightly.

Grate cheese

While toasts bake, grate 3 cups Gruyère and, if using, 1 tbs Parmesan. Mix cheeses together and keep ready.

Assemble and broil

Preheat the broiler. Ladle the hot soup into ovenproof bowls (ramekins or crocks) leaving 1/2" headspace. Place 1–2 toasted baguette slices on top of each bowl (or float them), then mound a generous handful of grated Gruyère over the toast to cover. Place bowls on a sheet pan and broil 2–4 minutes, watching closely, until cheese is bubbling and golden brown. Remove carefully; let sit 1–2 minutes before serving.

Optional: sprinkle chopped fresh parsley and a pinch of coarse sea salt over the melted cheese for brightness and finish. Serve hot, with extra toasts on the side.