Get ready for a flavor explosion with this Caramelized Onion and Mushroom Grilled Cheese! We're talking perfectly caramelized onions finished off with a splash of beef stock, sautéed mushrooms with thyme, and melty Swiss cheese. This isn't just your average grilled cheese; it's an adult version that's way better!
I haven't stopped craving this sandwich since I first made it. Seriously, it's SO good! My goal was to capture the cozy vibes of a bowl of French onion soup, complete with all those sweet, caramelized onions, gooey Swiss cheese, and a touch of crunch. And let me tell you, using a nice crusty sourdough bread is a game changer. It holds up perfectly against the juicy onion filling.
You might also like: Italian Sandwich, Crispy Chicken Sandwich, Chicken Parmesan Sandwich
Key InGredIENTS
- Onions - Yellow or white onions work great.
- Sugar - Granulated Sugar to help the caramelization of the onions.
- Beef Stock - A good quality beef stock for added flavor. Beef broth can be substituted if needed.
- Mushrooms - A mix of baby bellas and button mushrooms for flavor and texture. If you only have one, that works too.
- Fresh Thyme - To add a bit more flavor to the filling.
- Cheese - I love using Swiss cheese with this sandwich. Provolone is a great substitute.
See the recipe card below for the full list of ingredients and measurements.
How to Make Caramelized Onion and Mushroom Grilled Cheese
1. Heat oil and butter in a large skillet over medium-low heat. After the butter has melted, incorporate the sliced onions and a pinch of sugar. Sauté the onions, stirring occasionally to avoid burning, until they are caramelized, which should take about 20-30 minutes. Once the onions begin to soften, season with a pinch of salt.
The onions need to cook slowly so that they become tender, and their natural sugars can caramelize. Be sure to watch the heat to ensure the onions do not burn. If the onions are browning too fast, turn the heat down.
You will know the onions are done when they have turned a rich browned color and are tender.
2. Remove from the pan and add in 1 tablespoon of olive oil. Add in the sliced mushrooms and sauté until browned. Add the onions back to the pan. Season with salt, pepper and fresh thyme. Next add in 3 tablespoons of beef stock. Stir until well combined. Remove from the pan and set aside.
3. Spread the softened butter on one side of each piece of bread. Place cheese on each piece of bread (each sandwich will get 2 slices of cheese) and top with the caramelized onions and mushrooms. Put the sandwiches together and heat up a large cast iron skillet over medium heat.
4. Cook each sandwich until golden browned and the cheese is melted. Flipping as needed. Enjoy!
Why add sugar to the onions?
Caramelizing onions is a time-consuming process. They naturally contain sugars that caramelize upon slow cooking, eliminating the need for added sugar. However, I prefer to expedite the process by including sugar. Alternatively, one can forgo the sugar and simply extend the cooking time of the onions.
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📖 Recipe
Caramelized Onion and Mushroom Grilled Cheese
Ingredients
- 1 large onion thinly sliced
- 2 tablespoons olive oil
- 4 tablespoons butter
- 1 pinch sugar
- 3 tablespoons beef stock
- 8 mushrooms, button & baby bellos sliced
- ½ teaspoon fresh thyme
- as needed pepper
- ½ teaspoon salt
- 4 slices bread like sourdough
- 4 slices swiss cheese
Instructions
- Thinly slice the onions into half-moons. Place a large skillet over medium heat and add in 1 tablespoon of olive oil and 1 tablespoon of butter. Once hot add in the onions and a pinch of sugar.
- Sauté, stirring occasionally to prevent burning until caramelized. This will take 20-30 minutes. When the onions have started to soften add in salt. You will know the onions are done when they have turned a rich browned color and are tender.
- Remove from the pan and add in 1 tablespoon of olive oil. Add in the sliced mushrooms and sauté until browned. Add the onions back to the pan. Season with pepper and fresh thyme. Next add in 3 tablespoons of beef stock. Stir until well combined. Remove from the pan and set aside.
- Spread the remaining butter on one side of each piece of bread. Place cheese on each piece of bread (each sandwich will get 2 slices of cheese) and top with the caramelized onions and mushrooms. Put the sandwiches together and heat up a large cast iron skillet over medium heat.
- Cook each sandwich until golden browned and the cheese is melted. Flipping as needed. Enjoy!
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