Sourdough French Onion Grilled Cheese

Featured in: Vegetarian Picks

This sourdough sandwich blends deeply caramelized onions with layers of melted Gruyère and Swiss cheeses. The preparation begins by gently cooking sliced onions with butter, sugar, and thyme until golden and tender. These flavorful onions are then combined with Dijon mustard on crisp sourdough bread, topped with cheese, and grilled to a golden brown. The result is a rich, savory sandwich that carries the essence of French onion flavors in every bite. Ideal for a comforting main dish served warm.

Updated on Mon, 16 Feb 2026 08:21:42 GMT
A golden sourdough sandwich filled with caramelized onions and melted Gruyère, inspired by French onion soup. Save
A golden sourdough sandwich filled with caramelized onions and melted Gruyère, inspired by French onion soup. | ovenharmony.com

This Sourdough French Onion Grilled Cheese Sandwich is a decadent twist on classic grilled cheese, combining caramelized onions, melty Gruyère, and crispy sourdough for a rich, savory sandwich inspired by French onion soup. This vegetarian recipe yields 2 sandwiches and brings a touch of French-American flair to your table.

A golden sourdough sandwich filled with caramelized onions and melted Gruyère, inspired by French onion soup. Save
A golden sourdough sandwich filled with caramelized onions and melted Gruyère, inspired by French onion soup. | ovenharmony.com

With a preparation time of 20 minutes and a cooking time of 30 minutes, this medium-difficulty dish is perfect for a special lunch or a comforting dinner. The blend of sweet caramelized onions and sharp cheeses creates a sophisticated flavor profile that elevates the humble grilled cheese.

Ingredients

  • For the Caramelized Onions
  • 2 tablespoons unsalted butter
  • 2 large yellow onions, thinly sliced
  • 1 teaspoon sugar
  • 1/2 teaspoon salt
  • 1 teaspoon fresh thyme leaves (optional)
  • 2 tablespoons dry white wine or sherry (optional)
  • For the Sandwiches
  • 4 slices sourdough bread
  • 1 tablespoon Dijon mustard
  • 1 cup (100 g) Gruyère cheese, grated
  • 1/2 cup (50 g) Swiss cheese, grated
  • 2 tablespoons unsalted butter, softened
  • Freshly ground black pepper, to taste
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Instructions

1. Prepare the Caramelized Onions
Melt 2 tablespoons butter in a large skillet over medium heat. Add sliced onions, sugar, and salt. Cook, stirring frequently, until onions are golden and deeply caramelized, about 20–25 minutes. Stir in thyme and deglaze with white wine or sherry, scraping up any browned bits. Cook until liquid evaporates. Set aside.
2. Assemble the Sandwiches
Spread Dijon mustard on one side of each bread slice. Top two slices with half the Gruyère and Swiss cheeses, then evenly distribute the caramelized onions. Sprinkle with black pepper and top with remaining cheese. Cover each with a remaining bread slice, mustard side facing in.
3. Grill the Sandwiches
Spread softened butter on the outside of each sandwich. Heat a skillet or griddle over medium-low heat. Place sandwiches in the skillet and cook until golden brown and crisp, about 3–4 minutes per side, pressing gently with a spatula to help cheese melt. Remove from heat, let rest 1 minute, then slice and serve.

Zusatztipps für die Zubereitung

For extra flavor, you can add a pinch of garlic powder to the onions while they are caramelizing.

Varianten und Anpassungen

If you cannot find Gruyère, you can substitute it with Emmental or a sharp white cheddar cheese.

Serviervorschläge

Serve these sandwiches with a fresh side salad or a hot bowl of tomato soup. For a wine pairing, try a dry white like Sauvignon Blanc.

Crispy sourdough bread oozing with Swiss and Gruyère cheese, layered with sweet caramelized onions. Save
Crispy sourdough bread oozing with Swiss and Gruyère cheese, layered with sweet caramelized onions. | ovenharmony.com

Each serving of this sandwich contains 540 calories, 30g of total fat, 46g of carbohydrates, and 21g of protein. Enjoy this rich and savory meal that perfectly captures the essence of classic French onion soup in a crispy, handheld format.

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Recipe FAQ

How do I caramelize onions perfectly?

Cook thinly sliced onions slowly over medium heat with butter, salt, and sugar, stirring frequently until they turn deep golden and soft, about 20-25 minutes.

Can I substitute Gruyère cheese?

Yes, Emmental or sharp white cheddar work well to maintain melty texture and complementary flavors.

What bread is ideal for this sandwich?

Use sturdy sourdough bread for a crisp outside and hearty texture that holds the fillings well.

How should I grill the sandwich for best results?

Butter the outside slices and grill on medium-low heat, pressing gently until the bread is golden and cheese melts, about 3-4 minutes per side.

Are there any suggested pairings?

This sandwich pairs wonderfully with a fresh salad or tomato soup; a dry white wine like Sauvignon Blanc complements the flavors nicely.

Sourdough French Onion Grilled Cheese

Savory sourdough sandwich featuring caramelized onions, Gruyère, and Swiss cheese with a crispy finish.

Prep duration
20 min
Cook duration
30 min
Complete duration
50 min
Created by Claire Johnson

Classification Vegetarian Picks

Complexity Medium

Heritage French-American

Output 2 Portions

Dietary considerations Meat-free

Components

Caramelized Onions

01 2 tablespoons unsalted butter
02 2 large yellow onions, thinly sliced
03 1 teaspoon sugar
04 1/2 teaspoon salt
05 1 teaspoon fresh thyme leaves
06 2 tablespoons dry white wine or sherry

Sandwiches

01 4 slices sourdough bread
02 1 tablespoon Dijon mustard
03 1 cup grated Gruyère cheese
04 1/2 cup grated Swiss cheese
05 2 tablespoons softened unsalted butter
06 Freshly ground black pepper to taste

Directions

Phase 01

Caramelize the Onions: Melt 2 tablespoons butter in a large skillet over medium heat. Add sliced onions, sugar, and salt. Cook, stirring frequently, until onions are golden and deeply caramelized, approximately 20 to 25 minutes. Stir in thyme and deglaze with white wine or sherry, scraping up any browned bits from the pan bottom. Cook until liquid evaporates completely. Set aside.

Phase 02

Assemble the Sandwiches: Spread Dijon mustard on one side of each bread slice. Top two slices with half the Gruyère and Swiss cheeses, then evenly distribute the caramelized onions. Sprinkle with black pepper and top with remaining cheese. Cover each with the remaining bread slice, mustard side facing inward.

Phase 03

Grill the Sandwiches: Spread softened butter on the outside of each sandwich. Heat a skillet or griddle over medium-low heat. Place sandwiches in the skillet and cook until golden brown and crisp, approximately 3 to 4 minutes per side, pressing gently with a spatula to facilitate cheese melting. Remove from heat, let rest 1 minute, then slice and serve.

Necessary tools

  • Large skillet
  • Spatula
  • Grater
  • Bread knife
  • Cutting board

Allergy details

Review each component for potential allergens and consult healthcare professionals if you're unsure about ingredients.
  • Contains wheat from bread
  • Contains milk proteins from butter and cheese
  • May contain mustard allergens
  • Verify bread and cheese labels for additional potential allergens

Nutritional information (each portion)

These values are approximate guidelines only and shouldn't replace professional medical guidance.
  • Energy: 540
  • Fats: 30 g
  • Carbohydrates: 46 g
  • Proteins: 21 g