ORIGINAL RECIPE FOUND HERE
3 tablespoons salted butter
2 yellow onions, thinly sliced
kosher salt and black pepper
3/4 cup apple cider
1 tablespoon fresh thyme leaves
1 tablespoon chopped fresh sage
1 pinch crushed red pepper flakes
4 slices prosciutto
8 slices sourdough bread
2 tablespoons extra virgin olive oil or butter
1 1/2 cups shredded fontina cheese
1 1/2 cups shredded gouda or white cheddar cheese
1 honeycrisp apple, thinly sliced
Melt 2 tablespoons butter in a large skillet over medium-high heat. Add the onions and cook for 3 minutes, until softened. Add half the apple cider, season with salt and pepper, and continue cooking for another 5 minutes, until the cider has mostly evaporated. Add the remaining cider and cook another 5 minutes or until the onions are golden and caramelized. Add the thyme, sage, and crushed red pepper, cook another minute. Remove from heat.
In a large skillet set over medium heat, cook the prosciutto until crisp, about 2 minutes per side. Remove from the skillet.
Brush the outside of each slice of bread with olive oil or butter. On the inside of half of the slices of bread, evenly layer the cheeses, onion, apples, and prosciutto. Add the top piece of bread, olive oil side facing up.
I baked the sandwiches in a 425-degree Fahrenheit preheated oven for 5 minutes, flipping the sandwiches over, and then baked for another 5-7 minutes until the bread was golden brown and the cheese was melty.