# What You'll 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 prepared above
# How-To Steps:
01 - Melt 2 tablespoons of butter in a large skillet over medium-low heat. Add sliced onions, salt, and pepper. Cook, stirring occasionally, for 25 to 30 minutes until onions turn deep golden and caramelized. Stir in sugar and balsamic vinegar if desired; continue cooking for 2 to 3 minutes, then remove from heat.
02 - Arrange bread slices and spread one side of each slice with softened butter. Place two slices butter-side down, evenly layer half the grated Gruyère on top of each. Add caramelized onions over the cheese, then sprinkle the remaining Gruyère. Close sandwiches with the remaining bread slices, butter-side up.
03 - Heat a nonstick skillet or griddle over medium heat. Place sandwiches in the skillet and cook for 3 to 4 minutes per side, pressing gently until bread is golden brown and cheese melts. Lower the heat if bread browns too fast before the cheese is fully melted.
04 - Slice sandwiches and serve immediately while warm.