Mushroom Onion Gouda Grilled Cheese

INGREDIENTS:

8 slices sourdough bread
1 lb. mushrooms, sliced
2 large onions, thinly sliced
8 slices Gouda cheese
4 tbsp. butter, softened
2 tbsp. olive oil
Salt and black pepper, to taste

DIRECTIONS:

Heat the olive oil in a large skillet over medium heat. Add the onions with a pinch of salt and cook, stirring occasionally, for 15 to 20 minutes until deeply golden and caramelized. Add the sliced mushrooms, season with salt and black pepper, and continue cooking for about 10 minutes, until the mushrooms are browned and all of their liquid has evaporated.
Spread the softened butter on one side of each slice of sourdough bread. Place 1 slice, butter side down, in a skillet over medium heat. Layer with 1 slice of Gouda cheese, a generous spoonful of the mushroom and onion mixture, and another slice of Gouda cheese. Top with a second slice of bread, butter side up.
Cook for 3 to 4 minutes, or until the bread is golden brown and crisp. Carefully flip the sandwich and cook for another 3 to 4 minutes …