Sourdough French Onion Grilled Cheese (Printable)

Sourdough bread layered with caramelized onions and melted Gruyère for a rich, savory meal.

# What You Need:

→ 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, optional
06 - 2 tablespoons dry white wine or sherry, optional

→ Sandwich Assembly

07 - 4 slices sourdough bread
08 - 1 tablespoon Dijon mustard
09 - 1 cup grated Gruyère cheese
10 - 1/2 cup grated Swiss cheese
11 - 2 tablespoons unsalted butter, softened
12 - Freshly ground black pepper to taste

# Steps:

01 - 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 to 25 minutes. Stir in thyme and deglaze with white wine or sherry, scraping up any browned bits. Cook until liquid evaporates. Set aside.
02 - 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 inward.
03 - 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 to 4 minutes per side, pressing gently with a spatula to help cheese melt. Remove from heat, let rest 1 minute, then slice and serve.

# Expert Advice:

01 -
  • The slow-caramelized onions provide a deep, savory sweetness.
  • Gruyère and Swiss cheeses create the perfect gooey, melted center.
  • Toasted sourdough adds a satisfying crunch and a hint of tanginess.
02 -
  • Use medium-low heat when grilling the sandwich to ensure the cheese melts completely before the bread gets too dark.
  • Grate your own cheese for a smoother melt compared to pre-shredded varieties.
  • Let the sandwich rest for one minute after cooking to allow the cheese to set slightly for cleaner slicing.
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