Caramelized Onion Gruyère Cheese (Printable)

Sourdough grilled to golden perfection with caramelized onions and melted Gruyère cheese.

# What You Need:

→ Caramelized Onions

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

→ Sandwich

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

# How-To:

01 - Melt 2 tbsp butter in a large skillet over medium-low heat. Add thinly sliced onions, salt, and pepper. Cook while stirring occasionally for 25 to 30 minutes until onions are deeply golden and caramelized. Stir in optional sugar and balsamic vinegar, cooking for 2 to 3 more minutes. Remove from heat.
02 - Lay out bread slices and spread one side of each slice with softened butter. Place two slices butter-side down and evenly distribute half the grated Gruyère on top. Spoon caramelized onions over the cheese, then cover with remaining Gruyère. Close sandwiches with remaining bread slices, butter-side up.
03 - Heat a nonstick skillet or griddle over medium heat. Place sandwiches in skillet and cook for 3 to 4 minutes per side, pressing gently, until bread is golden brown and cheese is melted. Lower heat if bread browns too quickly before cheese melts.
04 - Slice sandwiches in half and serve immediately.

# Expert Advice:

01 -
  • Those caramelized onions taste like you spent hours in the kitchen, but the active work is minimal.
  • The contrast between crispy-golden bread and oozing melted cheese with sweet, savory onions hits every comfort note at once.
  • It's fancy enough for guests but simple enough that you'll make it on random weeknights.
02 -
  • Do not use medium heat or higher for caramelizing onions—they'll burn before they develop that deep sweetness.
  • Grating your own Gruyère instead of buying pre-shredded makes a visible difference in how smoothly it melts.
  • The butter on the outside of the bread needs to make direct contact with the skillet, or you'll end up with a soggy bread interior instead of a crispy exterior.
03 -
  • If you make the caramelized onions ahead of time, they actually taste better the next day once the flavors have settled and deepened.
  • Pressing gently on the sandwich while it cooks helps the cheese melt more evenly and keeps everything from sliding around, but don't press so hard that you squeeze out all the filling.
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