Sourdough French Onion Cheese (Printer View)

Savory grilled sandwich with caramelized onions, Gruyère, and crisp sourdough bread for a flavorful bite.

# 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

→ 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

# Method:

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, approximately 20 to 25 minutes. Stir in thyme and deglaze with white wine or sherry, scraping up browned bits from the skillet. Continue cooking until liquid evaporates completely. Set aside.
02 - Spread Dijon mustard on one side of each bread slice. Top two slices with half the Gruyère and Swiss cheeses, then distribute caramelized onions evenly across the cheese. 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, 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 immediately.

# Expert Advice:

01 -
  • The caramelized onions do all the heavy lifting, transforming from sharp to honeyed while you barely lift a finger.
  • Gruyère and Swiss cheese create this perfect creamy-nutty layer that makes you forget you're eating something so simple.
  • Sourdough's tang cuts through the richness like a best friend keeping you honest about what really matters.
02 -
  • Don't skip the resting time on the caramelized onions—I learned this the hard way by rushing them at 15 minutes and wondering why they tasted sharp instead of sweet, when really they just needed another 5 to 10 minutes to finish their transformation.
  • Medium-low heat on the grill is non-negotiable if you want melted cheese inside and crispy bread outside, not charred crust with cold cheese in the middle.
03 -
  • Press your sandwich gently but firmly with the spatula while it grills—this isn't violence, it's just encouraging the cheese to make contact with the heat so it melts evenly instead of staying thick and stubborn in the center.
  • If your cheese isn't melting as fast as you'd like, cover the skillet with a lid for the last minute of cooking on each side, trapping heat and steam that softens everything beautifully.
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