Sourdough Grilled Cheese Onions (Printable)

Tangy sourdough, rich Gruyere, and caramelized onions combine for a melty, flavorful sandwich.

# What You'll Need:

→ Bread & Cheese

01 - 4 slices sourdough bread
02 - 5 oz Gruyere cheese, grated or thinly sliced

→ Onions

03 - 1 large yellow onion, thinly sliced
04 - 1 tablespoon unsalted butter
05 - 1 teaspoon olive oil
06 - 1/4 teaspoon salt
07 - 1/2 teaspoon sugar

→ For Grilling

08 - 2 tablespoons unsalted butter, softened

→ Optional Additions

09 - Fresh thyme leaves or black pepper to taste

# Step-by-step Directions:

01 - Heat 1 tablespoon butter and olive oil in a skillet over medium heat. Add sliced onions and salt. Cook, stirring occasionally, for 15-18 minutes until golden brown and deeply caramelized. Add sugar halfway through if desired for enhanced sweetness. Set aside.
02 - Lay out sourdough slices. Butter one side of each slice generously.
03 - Place half the cheese on the unbuttered side of two bread slices. Top each with half the caramelized onions, then sprinkle with thyme or black pepper if using. Cover with remaining cheese and top with the other bread slices, buttered side facing outward.
04 - Heat a large skillet or griddle over medium-low heat. Place sandwiches in the pan. Cook for 3-4 minutes per side, pressing gently, until bread is golden brown and cheese is fully melted.
05 - Remove from pan and let rest for 1 minute. Slice diagonally and serve hot.

# Expert Advice:

01 -
  • The sourdough's subtle tang plays against rich, nutty Gruyere in ways that plain sandwich bread never could.
  • Caramelized onions are worth every minute of patient stirring—they turn sweet and deeply golden, nothing like raw onion bite.
  • This tastes restaurant-quality but comes together faster than ordering delivery.
02 -
  • Caramelizing onions actually takes longer than most recipes admit—17 to 20 minutes is more realistic than the promised 10, but rushing this step gives you sweet-ish onions instead of deeply caramelized ones.
  • The sandwich will taste better if you press it gently while cooking rather than aggressively flattening it, which squeezes out heat and prevents even melting.
03 -
  • If you're making these for more than two people, caramelize a larger batch of onions ahead of time and reheat them gently; they actually improve overnight as flavors deepen and meld.
  • Use a cast iron skillet if you have one—it holds heat more evenly and creates a more consistent golden brown crust across both sides of the sandwich.
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