Begin by heating a skillet over medium heat and adding 1 tablespoon of unsalted butter. Once melted, add the thinly sliced onions and sauté for about 10 minutes, stirring occasionally, until they turn a golden brown.

Next, add 1 tablespoon of balsamic vinegar and continue to cook for another 2-3 minutes, until the liquid reduces slightly and the onions are well-coated.

In the same skillet, use the residual heat to melt the remaining butter. Layer half of the shredded sharp cheddar cheese onto two slices of sourdough bread.

Spread the sweet caramelized onions evenly over the cheese, then add a layer of thinly sliced apples and pears. Finish by adding the rest of the cheese on top and cover each with another slice of sourdough.

Carefully transfer the assembled sandwiches to the skillet over medium heat. Grill each side for about 4-5 minutes, pressing down gently with a spatula.

When ready, remove the sandwiches from the skillet, allowing them to cool slightly before slicing them in half.

Serve warm with a side of fresh salad or a bowl of hearty soup.