In a skillet over medium heat, melt 1 tablespoon of unsalted butter. Add the thinly sliced onions and a pinch of salt; cook for about 10 minutes, stirring occasionally, until the onions turn golden brown and caramelized. Stir in a splash of balsamic vinegar and cook for an additional 2–3 minutes, then set this delicious mixture aside.

Using the same skillet, melt the remaining tablespoon of butter over medium heat. Take two slices of crusty sourdough bread and layer half of the shredded sharp cheddar cheese on one slice. Next, add the caramelized onions, followed by thinly sliced apple and pear, and top with the remaining cheddar cheese. Finally, cover with the other slice of bread.

Carefully place the assembled sandwich in the preheated skillet. Grill each side for 4–5 minutes, pressing down slightly to enhance the melt of the cheese. Cook until the bread is golden brown and crispy, and the cheese is beautifully melted.

Once grilled to perfection, remove the sandwich from the skillet and let it cool for a minute to avoid burning your tongue. Slice the sandwich diagonally and serve warm.