# Ingredient List:
→ Caramelized Onions
01 - 2 tablespoons unsalted butter
02 - 2 large yellow onions, thinly sliced
03 - 1 teaspoon sugar
04 - 1/2 teaspoon salt
05 - 1/4 teaspoon freshly ground black pepper
06 - 1 teaspoon fresh thyme leaves or 1/2 teaspoon dried thyme
07 - 1 tablespoon balsamic vinegar
→ Sandwich
08 - 4 slices sourdough or country-style bread
09 - 2 tablespoons unsalted butter, softened
10 - 1 cup shredded Gruyère cheese (about 3.5 ounces)
11 - 1 cup shredded mozzarella cheese (about 3.5 ounces)
12 - 2 teaspoons Dijon mustard
# Directions:
01 - Melt 2 tablespoons of unsalted butter in a large skillet set over medium heat. Add the thinly sliced onions, sugar, salt, and black pepper. Cook, stirring occasionally, until onions become deeply golden and caramelized, approximately 25 to 30 minutes.
02 - Incorporate the fresh thyme leaves and balsamic vinegar into the caramelized onions. Continue cooking for an additional 2 minutes until the mixture becomes fragrant. Remove from heat and set aside.
03 - Butter one side of each bread slice evenly. Apply Dijon mustard to the unbuttered side of two slices.
04 - On the mustard-spread side of bread slices, layer half of the shredded Gruyère and mozzarella cheeses. Top with a generous portion of caramelized onions, then distribute the remaining cheese evenly. Complete by placing the remaining bread slices on top, buttered side facing outward.
05 - Heat a clean skillet or griddle over medium-low heat. Place sandwiches in the pan and cook for 3 to 5 minutes on each side, pressing gently and flipping once, until bread achieves a golden crust and cheese is fully melted.
06 - Allow sandwiches to rest for 1 minute before slicing. Serve immediately while hot.
