Savory Caramelized Onion, Mushroom, and Swiss Toastie

In a skillet over medium-high heat, add 2 teaspoons of vegetable oil. When the oil is hot, add the thinly sliced onions and 1/2 teaspoon of salt. Cook until dark brown in color and softened, about 20-30 minutes. Lower the heat to medium halfway through the cooking time. If needed, add a tablespoon of water to aid with caramelization. Once caramelized, remove onions from skillet and place in a bowl.

In the same skillet, add the remaining 1 teaspoon of vegetable oil, sliced mushrooms, and the remaining 1/2 teaspoon of salt. Cook the mushrooms until softened, about 5 minutes. Remove mushrooms from the skillet, reserving any liquid in the skillet.

Preheat your oven's broiler. Spread softened butter on both sides of each sourdough bread slice. Place the bread slices on a baking sheet and broil for about 1 minute on each side or until lightly toasted.

To assemble the sandwich, place caramelized onions on one slice of bread, followed by mushrooms, and then 1/2 cup of shredded Swiss cheese. Gently place the sandwich back onto the baking sheet. Repeat with another slice of bread.

Place the baking sheet back into the oven and broil for 1-2 minutes, until the cheese is melted and bubbly. Remove from the oven and top each sandwich with the remaining toasted bread slices, pressing down gently. Slice the sandwiches in half and serve immediately.