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Ultimate French Onion Grilled Cheese Melt

A gourmet grilled cheese sandwich combining the rich flavors of French onion soup with sweet, slow-cooked caramelized onions and a blend of melty Gruyère and Fontina cheese on thick-cut sourdough.
Print Recipe
Prep Time 20 minutes
Cook Time 50 minutes
Total Time 1 hour 10 minutes
Servings: 2 sandwiches
Course: Dinner, Lunch
Cuisine: American, French Inspired
Calories: 750
Ingredients Equipment Method Notes

Ingredients
  

Caramelized Onions
  • 2 large yellow onions thinly sliced
  • 2 tbsp unsalted butter
  • 1 tbsp olive oil
  • 1 tbsp fresh thyme leaves chopped
  • 0.25 cup beef broth for deglazing
Sandwich Build
  • 4 slices thick-cut sourdough bread
  • 4 tbsp salted butter softened
  • 4 oz Gruyère cheese freshly grated
  • 4 oz Fontina cheese freshly grated

Equipment

  • Large heavy-bottomed skillet or Dutch oven
  • Cast iron skillet or griddle
  • Spatula
  • Box grater

Method
 

  1. Heat butter and oil in a large skillet over medium heat. Add sliced onions and cook for 10 minutes to soften.
  2. Reduce heat to medium-low. Add thyme, salt, and pepper. Cook slowly, stirring occasionally, for 30-45 minutes until deep golden brown and jammy.
  3. Increase heat to medium, add beef broth to deglaze the pan, scraping up browned bits. Cook until liquid evaporates. Remove onions from heat.
  4. Mix grated Gruyère and Fontina together. Butter one side of each bread slice.
  5. Place two bread slices butter-side down in a cold skillet. Top with cheese mixture, then caramelized onions. Top with remaining bread, butter-side up.
  6. Cook over medium-low heat for 4-6 minutes until the bottom is deep golden brown.
  7. Flip carefully and cook for another 3-5 minutes until the second side is browned and cheese is fully melted.
  8. Let rest for 1 minute before slicing. Garnish with fresh thyme sprigs.

Notes

Patience is key for the onions; do not rush them with high heat. Serve with a side of warm beef broth for dipping for the full French onion soup experience.