# What You'll Need:
→ For the Caramelized Onions
01 - 2 large yellow onions, thinly sliced
02 - 2 tablespoons unsalted butter
03 - 1 tablespoon olive oil
04 - 1/2 teaspoon salt
05 - 1/4 teaspoon freshly ground black pepper
06 - 1 teaspoon fresh thyme leaves (optional)
07 - 1 teaspoon balsamic vinegar (optional)
→ For the Sandwiches
08 - 4 slices rustic country bread
09 - 4 ounces Gruyère cheese, grated
10 - 1 tablespoon unsalted butter, softened
# Directions:
01 - Melt butter with olive oil in a large skillet over medium-low heat. Add sliced onions, salt, and pepper. Cook, stirring occasionally, until onions are deeply golden and caramelized, about 25-30 minutes. Stir in thyme and balsamic vinegar if using, and cook 1 minute longer. Remove from heat.
02 - Lay out bread slices. Evenly spread caramelized onions on two slices. Top each with half of the grated Gruyère. Place remaining bread slices on top to close sandwiches.
03 - Spread softened butter evenly on the outside of each sandwich.
04 - Heat a non-stick skillet or griddle over medium heat. Place sandwiches in the pan and cook until golden brown and cheese is melted, about 3-4 minutes per side. Press gently with spatula to ensure even toasting.
05 - Slice sandwiches in half and serve immediately.