In a medium skillet, heat 2 tablespoons of olive oil over medium heat. Add thinly sliced onions and a pinch of salt and pepper. Cook for about 15 minutes until golden brown and caramelized.

Remove the onions and add bacon strips to the same skillet. Cook on medium heat for 5-7 minutes until crispy and golden.

On a clean surface, layer one slice of bread, cheese, bacon, caramelized onions, another slice of cheese, and top with another slice of bread.

Spread unsalted butter on the outer sides of both slices of bread.

Preheat the skillet and grill the sandwich for about 4-5 minutes on each side until golden brown and cheese is melted.

Allow to cool for a minute, slice diagonally, and serve immediately.