Slow-Cooker French Onion Soup

Sweet slow-cooked onions get a brief stovetop browning before beef stock and sherry become a rich broth, finished with crisp baguette and bubbling Gruyère.

493 min

6 bowls

Six ceramic bowls of French onion soup are topped with toasted baguette and bubbling browned Gruyère.

Ingredients

4 lb yellow onions, halved and thinly sliced

4 tbsp unsalted butter

1 tsp kosher salt, divided

1/2 tsp freshly ground black pepper

1 tbsp fresh thyme leaves

8 cups low-sodium beef stock, divided

2 tbsp all-purpose flour

1/2 cup dry sherry

2 bay leaves

1 large baguette, cut into 12 slices 1/2 inch thick

2 tbsp olive oil

8 oz Gruyère cheese, coarsely grated

Equipment

5- to 6-quart slow cooker · Wide Dutch oven · Rimmed sheet pan · Six oven-safe bowls · Oven mitts

Watch the onions

The slow cooker softens and sweetens the onions; keep stirring during the stovetop finish so the deeper amber color does not turn scorched.

Serve carefully

Set each bowl on a heatproof plate and let it stand briefly; both the ceramic and the melted cheese stay very hot.

Soften the onions

01. Toss onions, butter, 1/2 tsp salt, thyme, and 1/2 cup stock in a 5- to 6-quart cooker so the onions are lightly coated.

02. Cover and cook on low for 7 hours, until the onions are collapsed, very soft, and tan-gold; keep the lid closed near the end.

Deepen and finish

03. Move onions and their liquid to a wide Dutch oven; stir over medium-high heat 8 to 12 minutes until glossy and deeper amber.

04. Stir in flour for 1 minute, then add sherry and scrape the browned fond until the alcohol aroma softens.

05. Add remaining stock, bay, and pepper. Simmer gently for 15 minutes, until the broth is lightly thickened and onion-sweet.

Toast and assemble

06. Brush baguette slices with olive oil and bake at 400 F for 8 to 10 minutes, turning once, until crisp and golden.

07. Discard bay leaves, stir in remaining salt, and taste the broth before filling six oven-safe bowls.

08. Top each bowl with two toast slices and grated Gruyère, spreading the cheese to the edges.

Broil and serve

09. Broil on a sheet pan for 2 to 4 minutes, watching until cheese bubbles and browns in spots.

10. Rest the bowls 2 minutes before serving; use oven mitts and remind diners the bowls are very hot.