French Onion Grilled Cheese

French Onion Grilled Cheese turns a favorite bowl of soup into a wonderfully satisfying sandwich. Sweet yellow onions slowly caramelize until they’re soft, golden, and almost jammy. A little thyme, Worcestershire sauce, and beef broth bring that familiar savory French onion flavor without making the filling soupy.

Between thick slices of sourdough, nutty Gruyère and mild provolone melt around the onions, creating a rich, stretchy center. Meanwhile, a light swipe of Dijon adds just enough brightness to balance every buttery bite.

The trick is simple: give the onions time, then toast the sandwiches over gentle heat so the bread turns crisp while the cheese melts completely. It’s an especially lovely lunch or cozy, no-fuss dinner with a green salad or a cup of soup. A classic grilled cheese, just dressed up enough to feel special.

Recipe Yield: 2 servings

INGREDIENTS

4 slices thick-cut sourdough bread (about 1/2-inch thick)
2 tbsp unsalted butter, softened
1 tsp Dijon mustard
4 oz Gruyère cheese, freshly shredded
2 oz provolone cheese, sliced or shredded
2 large yellow onions, thinly sliced
1 tbsp olive oil
1 tbsp unsalted butter
1/4 tsp kosher salt
1/8 tsp black pepper
2 tbsp low-sodium beef broth
1 tsp Worcestershire sauce
1 tsp fresh thyme leaves (or 1/4 tsp dried)

INSTRUCTIONS

1. Soften the onions:
Heat olive oil and 1 tbsp butter in a wide skillet over medium heat, then add onions and salt and cook for 5 minutes until softened.

2. Caramelize slowly:
Reduce heat to medium-low and cook for 30–40 minutes, stirring every few minutes, until the onions are deep golden brown and jammy, adding a splash of water if they begin to stick.

3. Build the flavor:
Stir in beef broth, Worcestershire sauce, thyme, and black pepper, then cook for 1–3 minutes until no loose liquid remains and transfer the onions to a bowl.

4. Prepare the bread:
Spread the outside of each sourdough slice with softened butter, then spread Dijon mustard on the inside of two slices.

5. Assemble the sandwiches:
Divide half the Gruyère and provolone between the two bottom slices, add the caramelized onions, then top with the remaining cheese and bread, keeping the buttered sides facing out.

6. Grill until golden:
Cook the sandwiches in the wiped skillet over medium-low heat for 3–5 minutes per side until golden and melted, covering briefly over low heat if the cheese needs more time.

7. Slice and serve:
Let the sandwiches rest for 1 minute, then slice in half and serve warm.

Helpful Tips to Perfect This Recipe

• Take your time with the onions: Deep caramelization creates the signature French onion flavor. Keep the heat gentle so the onions become sweet and golden without burning.
• Keep the bread crisp: Allow the broth to cook off completely before assembling. A concentrated, jammy onion filling delivers rich flavor without making the sourdough soggy.
• Make ahead for easier lunches: Prepare the caramelized onions up to 3 days ahead and refrigerate. Warm them before assembling, then grill the sandwiches fresh for the best melted cheese and crisp bread.