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Two stacked slices of Grilled Cheese with Caramelized Onions and Spinach.

Grilled Cheese with Caramelized Onions and Spinach

Grilled Cheese with Caramelized Onions and Spinach recipe! This grilled cheese sandwich is packed with caramelized onions, greens, and melty Cheddar cheese for a decadent addition to lunch.
Course Main
Cuisine N/A
Keyword caramelized onion, grilled cheese, onion, sandwich, spinach
Prep Time 10 minutes
Cook Time 40 minutes
0 minutes
Total Time 50 minutes
Servings 4 Sandwiches


  • 1 1/2 tablespoons vegetable oil
  • 2 medium red onions thinly sliced
  • Salt and pepper to taste
  • 8 slices sourdough or country bread
  • 2 tablespoons butter
  • 8 ounces Cheddar cheese sliced
  • 2 cups baby spinach leaves
  • 1/2 teaspoon red pepper flakes if desired
  • 1/3 cup mayonnaise


  • In a large pan, drizzle oil over medium low heat. Once heated, add the sliced onions. Reduce heat to low and cook, stirring occasionally, until a deep purple and caramelized, about 30 minutes. Sprinkle with salt and pepper. Transfer to a medium bowl and allow to cool.
  • Place a large skillet over medium low heat.
  • Spread butter over one side of each slice of bread. Cover half of the bread slices with a layer of cheese on the buttered side. Cover the cheese with a thin layer of caramelized onions and a few spinach leaves. If desired, season with some red pepper flakes. Top with another layer of cheese, then the remaining bread slices, butter side touching the cheese. Spread the top of each sandwich with mayonnaise.
  • Place a sandwich on the heated skillet, mayonnaise coated side down. Spread mayonnaise on the top of the sandwich. Cook until the bottom layer of cheese is melted and bread is golden brown. Flip and cook other side until melted and golden brown.
  • Serve immediately and repeat with remaining sandwiches.