# 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
07 - 1 teaspoon balsamic vinegar
→ For the Sandwiches
08 - 4 slices rustic country bread
09 - 4 ounces Gruyère cheese, grated
10 - 1 tablespoon unsalted butter, softened
# Preparation Steps:
01 - In a large skillet over medium-low heat, melt the butter with the olive oil. Add the sliced onions, salt, and pepper. Cook, stirring occasionally, until the onions are deeply golden and caramelized, about 25–30 minutes. Stir in thyme and balsamic vinegar and cook 1 minute longer. Remove from heat.
02 - Lay out the bread slices. Evenly spread caramelized onions on two slices. Top each with half of the grated Gruyère. Place the remaining bread slices on top to close the sandwiches.
03 - Butter the outside of each sandwich with the softened butter.
04 - Heat a non-stick skillet or griddle over medium heat. Place the sandwiches in the pan and cook until golden brown and the cheese is melted, about 3–4 minutes per side. Press gently with a spatula to ensure even toasting.
05 - Slice in half and serve immediately.