# What You’ll Need:
→ Bread & Cheese
01 - 4 slices sourdough bread
02 - 5 ounces Gruyere cheese, grated or thinly sliced
→ Onions
03 - 1 large yellow onion, thinly sliced
04 - 1 tablespoon unsalted butter
05 - 1 teaspoon olive oil
06 - 1/4 teaspoon salt
07 - 1/2 teaspoon sugar
→ For Grilling
08 - 2 tablespoons unsalted butter, softened
→ Optional Additions
09 - Fresh thyme leaves or black pepper to taste
# How to Make It:
01 - Heat 1 tablespoon butter and 1 teaspoon olive oil in a skillet over medium heat. Add sliced onions and salt. Cook, stirring occasionally, for 15-18 minutes until golden brown and deeply caramelized. Add sugar halfway through if desired for enhanced sweetness. Transfer to a plate and set aside.
02 - Lay out all four sourdough slices. Butter one side of each slice with softened butter.
03 - Place half the grated cheese on the unbuttered side of two bread slices. Distribute half the caramelized onions evenly over each portion of cheese. Sprinkle with fresh thyme leaves or black pepper if desired. Top with remaining cheese, then cover with the other two bread slices with buttered sides facing outward.
04 - Heat a large skillet or griddle over medium-low heat. Place assembled sandwiches in the pan. Cook for 3-4 minutes per side, pressing gently with a spatula, until bread achieves a golden-brown crust and cheese is completely melted.
05 - Transfer sandwiches to a cutting board and allow to rest for 1 minute. Slice diagonally and serve immediately while hot.