# What You Need:
→ Caramelized Onions
01 - 2 medium yellow onions, thinly sliced
02 - 2 tbsp unsalted butter
03 - 1/2 tsp kosher salt
04 - 1/4 tsp freshly ground black pepper
05 - 1/2 tsp sugar (optional)
06 - 1 tsp balsamic vinegar (optional)
→ Sandwich
07 - 4 slices rustic sourdough or country bread
08 - 2 tbsp unsalted butter, softened
09 - 5 oz Gruyère cheese, grated
10 - Caramelized onions (from above)
# Directions:
01 - Melt 2 tablespoons of butter in a large skillet over medium-low heat. Add the sliced onions, kosher salt, and black pepper. Cook, stirring occasionally, for 25 to 30 minutes until the onions turn golden brown and are deeply caramelized. If desired, stir in sugar and balsamic vinegar, cooking for an additional 2 to 3 minutes. Remove from heat.
02 - Arrange the bread slices and spread softened butter on one side of each. Place two slices butter-side down, distribute half of the grated Gruyère evenly over them, then layer with caramelized onions. Top with the remaining Gruyère and cover with the remaining bread slices, butter-side up.
03 - Heat a nonstick skillet or griddle over medium heat. Place the assembled sandwiches onto the skillet and cook for 3 to 4 minutes per side, pressing gently, until the bread is golden and the cheese has melted. Lower the heat if the bread browns too quickly before the cheese melts.
04 - Slice the sandwiches and serve immediately for best texture and flavor.