Sourdough Grilled Cheese Onions (Print version)

Melty sourdough sandwich with rich Gruyere and sweet caramelized onions, grilled to golden perfection.

# 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

# Steps:

01 - Heat 1 tablespoon butter and 1 teaspoon 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 and butter one side of each slice with softened butter.
03 - Place half the Gruyere on the unbuttered side of two bread slices. Top each with half the caramelized onions, then sprinkle with thyme or black pepper if desired. Cover with remaining cheese and top with remaining bread slices, buttered side facing outward.
04 - Heat a large skillet or griddle over medium-low heat. Place assembled 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 sandwiches from pan and let rest for 1 minute. Slice diagonally and serve immediately while hot.

# Cooking tips:

01 -
  • It transforms a weeknight staple into something fancy enough to impress without requiring any fancy techniques.
  • The caramelized onions do most of the heavy lifting—sweet, complex, and they make the whole sandwich taste intentional.
  • Sourdough's tanginess cuts through the richness of the Gruyere in a way that feels balanced and grown-up.
02 -
  • Don't rush the onions—the temptation is real, but turning up the heat or skipping the stirring will give you burned onion bits instead of sweet caramel, and that's a different (worse) sandwich.
  • Slice your onions as uniformly thin as you can manage; uneven sizes cook at different rates and you'll end up with some pieces that are barely softened while others turn to mush.
  • Use medium-low heat for cooking the sandwich itself—I learned this the hard way when I burned three in a row trying to rush the process.
03 -
  • Grate your cheese while the onions are still cooking so it's ready to go; cold grated cheese melts faster and more evenly than slices.
  • If your skillet seems too hot while cooking, slide the sandwich to a cooler spot and adjust your heat down—burnt crust with cold cheese inside is fixable by moving, not by rushing.
  • Make these in pairs if you're feeding a crowd; they cook better with space around them and it's easier to manage the heat.
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