Caramelized Onion Gruyère Cheese (Printable)

Golden, buttery bread layered with rich caramelized onions and melted nutty Gruyère cheese.

# What You'll Need:

→ Caramelized Onions

01 - 2 medium yellow onions, thinly sliced
02 - 2 tablespoons unsalted butter
03 - 1/2 teaspoon kosher salt
04 - 1/4 teaspoon freshly ground black pepper
05 - 1/2 teaspoon sugar (optional)
06 - 1 teaspoon balsamic vinegar (optional)

→ Sandwich

07 - 4 slices rustic sourdough or country bread
08 - 2 tablespoons unsalted butter, softened
09 - 5 ounces Gruyère cheese, grated
10 - Caramelized onions prepared above

# How to make it:

01 - Melt 2 tablespoons unsalted butter in a large skillet over medium-low heat. Add sliced onions, salt, and pepper. Cook, stirring occasionally, for 25 to 30 minutes until onions turn deep golden and caramelized. Stir in sugar and balsamic vinegar if using, then cook for an additional 2 to 3 minutes. Remove from heat.
02 - Spread softened butter on one side of each bread slice. Place two slices butter-side down, evenly distribute half the grated Gruyère on top, spoon caramelized onions over the cheese, then layer remaining Gruyère. Close each sandwich with remaining bread slices, butter-side up.
03 - Heat a nonstick skillet or griddle over medium heat. Cook sandwiches for 3 to 4 minutes per side, pressing gently, until bread is golden brown and cheese fully melts. Lower heat if bread browns too quickly.
04 - Slice sandwiches and serve immediately.

# Recipe Expert Tips:

01 -
  • Those caramelized onions are pure magic—sweet, jammy, and they transform ordinary bread and cheese into something restaurant-worthy.
  • It's genuinely easy but tastes like you spent way more time than you actually did.
  • Gruyère's nutty flavor pairs with the onions in a way that feels both comforting and sophisticated.
02 -
  • Don't rush the onions—I learned this the hard way by turning up the heat and ending up with burnt edges instead of that glossy caramel. Low and slow every time.
  • The butter on the outside of the bread makes all the difference; it's what gives you that perfect golden crust instead of a pale, sad sandwich.
03 -
  • A splash of balsamic vinegar in the onions at the end rounds out all those flavors and prevents them from tasting one-note sweet.
  • If you want to get fancy, add a few fresh thyme leaves to the onions while they're cooking—it's a small touch that feels very French.
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