Apple & Caramelized Onion Grilled Cheese Recipe

Prep onions

Peel and thinly slice onions into half-moons so they measure about 2 cups packed.

Heat a medium skillet over medium heat. Add 1 tablespoon olive oil and 1 teaspoon butter; when butter melts and begins to foam, add the sliced onions in an even layer.

Cook onions, stirring every 2–3 minutes, adjusting heat as necessary so they soften and brown slowly without burning. After about 8–12 minutes the onions will be soft and beginning to brown.

Sprinkle 1 teaspoon granulated sugar over the onions to help with caramelization. Continue cooking and stirring every few minutes until deeply golden, about 8–12 more minutes (total 18–25 minutes). If pan gets too dry, add 1–2 teaspoons water to deglaze.

Stir in 3 tablespoons balsamic vinegar, 1 tablespoon brown sugar, 2 tablespoons water, 1 teaspoon salt and 1 teaspoon black pepper. Reduce heat to low and simmer until liquid thickens and onions become jammy, about 4–6 minutes.

Taste and adjust seasoning. Remove from heat and let cool slightly. The jam will thicken as it cools. Use immediately or store in an airtight container in the fridge up to 7 days.

Prepare apples: core and thinly slice 1 large apple (about 10–12 thin slices). If preferred, toss slices with a light squeeze of lemon to prevent browning.

Lay out 4 slices of sourdough as the bottom pieces. Spread about 2 tablespoons of softened butter evenly on the outside of the remaining 4 slices (these will be the top of each sandwich).

On each bottom slice, layer the fillings in this order: a heaping tablespoon of balsamic caramelized onion jam (about 1 tbsp), a generous handful (about 1/2 cup) of shredded or sliced white cheddar, several thin apple slices arranged in a single layer (about 8–10% of the apple per sandwich), and about 2 tablespoons crumbled feta sprinkled evenly. Top with the remaining white cheddar (another 1/4 cup) to ensure good melt and close the sandwich with the buttered slice on top, buttered side facing out.

Heat a large nonstick or cast-iron skillet over medium-low to medium heat. Place sandwiches in the skillet (work in batches if necessary). Cook gently for 3–4 minutes per side, pressing lightly with a spatula or using a sandwich press; adjust heat so bread browns slowly and cheese melts without burning the bread.

When the first side is golden brown and the cheese starts to melt, flip and cook the other side another 3–4 minutes until golden and cheese is fully melted. If the exterior browns too fast before cheese melts, lower the heat and cover the pan for 1–2 minutes to trap heat.

Remove sandwiches to a cutting board and let rest 1 minute. Cut each sandwich in half on the diagonal and serve immediately.