Melt 2 tablespoons butter in a large skillet over medium-high heat. When the oil shimmers, add the onions and cook 3 minutes, until softened. Add half the apple cider, season with salt and pepper and continue cooking 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 the 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. 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.Place the sandwiches, 1-2 at a time, in the skillet and cook until golden on each side, about 3-5 minutes per side. During the last minute of cooking, add 1/2 tablespoon butter and 2 sage leaves. Repeat with the remaining 2 sandwiches. Serve immediately, topping with the crispy sage. EAT and ENJOY.