# Components:
→ Caramelized Onions
01 - 2 tablespoons unsalted butter
02 - 2 large yellow onions, thinly sliced
03 - 1 teaspoon granulated 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 (approximately 3.5 ounces)
11 - 1 cup shredded mozzarella cheese (approximately 3.5 ounces)
12 - 2 teaspoons Dijon mustard
# Directions:
01 - In a large skillet over medium heat, melt 2 tablespoons unsalted butter. Add sliced onions, sugar, salt, and black pepper. Cook, stirring occasionally, until onions are golden brown and deeply caramelized, about 25 to 30 minutes.
02 - Stir in thyme leaves and balsamic vinegar. Cook for an additional 2 minutes until fragrant. Remove skillet from heat and set aside.
03 - Butter one side of each bread slice evenly. Spread Dijon mustard on the unbuttered side of two slices.
04 - Layer half of the Gruyère and mozzarella cheeses onto the mustard-covered side of the bread. Add a generous spoonful of caramelized onions on top, then cover with the remaining cheese. Place 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 skillet and cook for 3 to 5 minutes per side, pressing gently and flipping once, until bread is golden brown and cheese is fully melted.
06 - Allow sandwiches to rest for 1 minute before slicing. Serve warm.
