Crafting the perfect Caramelized Onion Grilled Cheese is a straightforward process. Follow these step-by-step instructions to create this tasty sandwich:

1. Caramelize the Onions: In a large skillet over medium heat, add olive oil and butter. Once melted, add the sliced onions and a pinch of salt. Stir to coat the onions.
2. Cook Slowly: Allow the onions to cook slowly for about 15-20 minutes. Stir occasionally until they turn golden brown and sweet.
3. Prepare the Bread: Meanwhile, take your slices of bread and butter one side of each slice. This will help create a nice golden crust while grilling.
4. Assemble the Sandwich: Once the onions are caramelized, remove them from the skillet. On the non-buttered side of one slice of bread, add a generous portion of cheese, followed by a layer of caramelized onions, then more cheese on top.
5. Top and Grill: Cover with another slice of bread, buttered side out. Repeat with remaining bread, making additional sandwiches as needed.
6. Grill: In the same skillet, add the sandwiches. Cook for 3-5 minutes on each side or until the bread is golden brown and the cheese melts. Keep the heat medium to avoid burning the bread while ensuring the cheese melts thoroughly.
7. Slice and Serve: Once cooked, remove the sandwiches from the skillet. Slice in half and serve immediately.

These steps ensure that you will create a delightful sandwich bursting with flavor.