# What You Need:
→ Caramelized Onions
01 - 2 large yellow onions, thinly sliced
02 - 2 tablespoons unsalted butter
03 - 1 tablespoon olive oil
04 - 1/2 teaspoon kosher salt
05 - 1/2 teaspoon granulated sugar
06 - 1/4 teaspoon freshly ground black pepper
07 - 1/2 teaspoon fresh thyme leaves (optional)
08 - 1 tablespoon balsamic vinegar (optional)
→ Sandwich Assembly
09 - 4 slices sourdough or country-style bread
10 - 6 ounces Gruyère cheese, grated
11 - 2 ounces Swiss or Emmental cheese, grated
12 - 2 tablespoons mayonnaise or softened butter, for spreading
# How to Cook:
01 - In a large skillet, melt butter with olive oil over medium-low heat. Add the sliced onions, salt, sugar, and black pepper. Stir regularly and cook until the onions become deep golden and very soft, about 25 to 30 minutes. In the final minutes, incorporate thyme leaves and balsamic vinegar if using.
02 - Combine the grated Gruyère and Swiss cheeses in a bowl and toss until well mixed.
03 - Spread mayonnaise or softened butter evenly on one side of each bread slice.
04 - Flip the bread slices so the spread is facing down. On two slices, arrange half of the cheese mixture on the unbuttered side, top with caramelized onions, then sprinkle remaining cheese. Close with remaining bread slices, spread side facing outward.
05 - Heat a clean skillet over medium heat. Place sandwiches in the skillet and cook 3 to 4 minutes per side, pressing gently with a spatula, until bread is golden and crisp and cheese is thoroughly melted.
06 - Remove sandwiches from the skillet. Let stand for 1 to 2 minutes, then cut and serve hot.
