In a large skillet, melt 1 tablespoon of unsalted butter over medium heat. Add the sliced medium onion and season with a pinch of salt. Cook, stirring occasionally, until the onions turn golden brown and caramelized, about 10 minutes. Stir in a splash of balsamic vinegar and cook for another 2-3 minutes, allowing the flavors to meld before removing the onions from the skillet and setting them aside.

In the same skillet, melt the remaining tablespoon of butter over medium heat. While the butter melts, lay out two slices of sourdough bread. Start layering by placing half of the shredded sharp cheddar cheese on one slice, followed by a generous portion of the caramelized onions, then a layer of apple slices and pear slices. Top it off with the remaining cheese before placing the other slice of bread on top to form a sandwich.

Carefully place the assembled sandwich into the preheated skillet. Grill for about 4-5 minutes, or until the bread is golden brown and crispy. Use a spatula to gently press down on the sandwich for even grilling. Once the bottom is nicely browned, flip the sandwich over and grill the other side until the cheese is fully melted and the bread is golden brown.

After grilling, allow the sandwich to cool for a minute on a cutting board. Carefully slice the sandwich in half diagonally for a beautiful presentation. Serve the warm Pear & Apple Grilled Cheese with Caramelized Onions and enjoy the delicious blend of sweet, savory, and creamy flavors right away.