Heat 2 tablespoons of olive oil in a large skillet over medium heat. Add your thinly sliced yellow onions and cook for about 20 minutes, stirring occasionally, until they are translucent and starting to soften.

Add 2 tablespoons of butter and continue to cook for another 20 minutes, stirring frequently, until the onions caramelize into a golden-brown color.

Sprinkle a teaspoon of salt, a teaspoon of sugar, a pinch of cinnamon, and pepper over the onions. Cook for an additional 5 minutes to meld the flavors.

Add minced garlic and cook gently for additional flavor.

Pour in 1/4 cup of dry red wine to deglaze the pan, scraping any flavorful bits stuck to the bottom. Simmer for 5–7 minutes.

In a small bowl, combine 2 tablespoons of melted butter with a teaspoon each of dried rosemary and thyme. Brush this mixture on one side of each slice of sourdough bread.

Place two slices of sourdough bread butter-side down in the skillet. Layer caramelized onions and cheese on top. Add another slice of buttered bread.

Cook the sandwich for about 5 minutes on one side until golden brown, then flip and cook the other side for another 5 minutes.

Transfer the skillet to the broiler for a couple of minutes until the top is crispy. Enjoy your sandwich!