In a skillet, melt 1 tablespoon of unsalted butter over medium heat. Add the thinly sliced onions along with a pinch of salt, stirring occasionally for about 10 minutes until they soften and turn a beautiful golden brown. Drizzle in a splash of balsamic vinegar, continuing to cook for an additional 2-3 minutes until the onions are richly caramelized and aromatic.

Using the same skillet, melt the remaining butter over medium heat. Assemble the sandwich by layering half of the shredded sharp cheddar cheese on two slices of sourdough bread. On top of the cheese, add a generous amount of the caramelized onions, followed by the thinly sliced apple and pear. Finally, layer the rest of the cheese before topping each with another slice of bread.

Carefully place one sandwich in the hot skillet and grill for about 4-5 minutes, or until the bread is golden brown and the cheese begins to melt. Flip the sandwich using a spatula, ensuring it heats evenly. Repeat this process for the second sandwich in the remaining butter.

Once the Pear & Apple Grilled Cheese with Caramelized Onions is grilled to perfection, gently remove it from the skillet and allow it to cool for a minute. Slice each sandwich in half to reveal the ooey-gooey interior. Serve warm.