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French Onion Grilled Cheese

A grilled cheese sandwich filled with deep golden caramelized onions and melted Gruyère, griddled in mayonnaise for a crisp, browned crust.

sandwichvegetarianfrenchstovetop
Illustration of French Onion Grilled Cheese
Illustration

Ingredients

  • 4 tbsp unsalted butter
  • 1 lb yellow or Vidalia onions, peeled, halved and thinly sliced
  • kosher salt
  • black pepper
  • 2 tsp sherry, red-wine or white-wine vinegar, optional
  • 4 oz Gruyère cheese, grated
  • 4 slices bread, cut no wider than 1/2-inch thick
  • mayonnaise
  • water, a few tablespoons at a time

Steps

1Caramelize the onions

  1. Melt 2 tbsp butter in a large skillet over medium-high heat.
  2. Add 1 lb yellow or Vidalia onions.
  3. Season with kosher salt.
  4. Season with black pepper.
  5. Cover and cook, stirring once or twice, until the onions are softened, 3 to 5 minutes.
  6. Uncover and reduce the heat to medium-low.
  7. Cook, stirring occasionally, until deep golden brown, 20 to 25 minutes.
  8. If the onions look dry or like they might burn, add a few tablespoons of water at a time, scraping up any browned bits that are stuck to the bottom of the skillet.
  9. Deglaze the skillet with 2 tsp sherry vinegar or bourbon.
  10. Cook until the liquid has evaporated, about 1 minute.
  11. Transfer the onions to a medium bowl.
  12. Season to taste with kosher salt.
  13. Season to taste with black pepper.
  14. Wipe out the skillet, or wash it, if necessary.

2Assemble the sandwiches

  1. Add 4 oz Gruyère to the onions and stir to combine.
  2. Lay out 2 slices bread.
  3. Scoop half of the cheese-onion mixture onto each slice.
  4. Top with the remaining 2 slices bread.
  5. Press down gently.

3Griddle and serve

  1. Cover one slice of bread with mayonnaise on the outside of the sandwich (this will help the bread brown).
  2. Place the sandwiches mayonnaise side down in the skillet over medium heat.
  3. Cook until the bottoms turn golden brown, 3 to 4 minutes, reducing the heat to prevent the toast from darkening too quickly, if needed.
  4. While cooking the first side, layer mayonnaise over the top side.
  5. Flip the sandwiches and press down.
  6. Cook until the cheese has fully melted and the bottoms turn golden brown, 3 to 4 minutes.
  7. Serve immediately.