Introduction

The Swiss Mushroom Melt Sandwich combines rich caramelized onions, savory sautéed mushrooms, and melty Swiss cheese for an irresistible bite. This hearty sandwich is perfect for a comforting lunch or casual dinner.

A grilled sandwich with two thick, crispy golden-brown toasted bread slices stacked on top, sprinkled with green herbs and topped with a small bunch of fresh curly parsley. Between the bread layers, there is a thick layer of melted creamy cheese oozing out over a bed of cooked brown mushrooms which are soft and glossy, sitting on a white plate with a few green herbs scattered around. A fork is partially visible at the bottom left corner, resting on the white marbled surface. photo taken with an iphone --ar 4:5 --v 7

Ingredients

2 large yellow onions, thinly sliced
2 tablespoons olive oil (plus extra for mushrooms)
1 tablespoon butter (plus 2 tablespoons softened butter)
1 teaspoon brown sugar
1/2 teaspoon balsamic vinegar
Salt and freshly ground black pepper to taste
1 pound cremini mushrooms, sliced
2 cloves garlic, minced
1/4 cup dry white wine (optional)
1 tablespoon fresh thyme leaves
4 slices sourdough bread (or your favorite bread)
4 ounces Swiss cheese, thinly sliced
1 tablespoon Dijon mustard (optional)

Instructions

Step 1: Peel and thinly slice the yellow onions. Heat 2 tablespoons olive oil and 1 tablespoon butter in a large skillet over medium-low heat.
Step 2: Add the sliced onions to the skillet, stirring to coat. Cook slowly over low heat for 30-45 minutes, stirring occasionally, until deep golden brown and very soft. Reduce heat if onions brown too quickly.
Step 3: Stir in 1 teaspoon brown sugar and 1/2 teaspoon balsamic vinegar. Cook for 2-3 minutes until sugar dissolves and vinegar is absorbed. Season with salt and black pepper, then remove onions from the skillet and set aside.
Step 4: In the same skillet, heat 2 tablespoons olive oil over medium-high heat. Add sliced mushrooms in batches if needed to avoid overcrowding.
Step 5: Cook mushrooms, stirring occasionally, until browned and softened, about 8-10 minutes. Add minced garlic and thyme leaves; cook 1 more minute until fragrant.
Step 6: (Optional) Pour in dry white wine and scrape up browned bits. Let it reduce until almost evaporated. Season mushrooms with salt and pepper, then remove from heat and set aside.
Step 7: Spread softened butter on one side of each bread slice. Optionally, spread Dijon mustard on the other side of the bread for extra flavor.
Step 8: Layer Swiss cheese, caramelized onions, and sautéed mushrooms on the unbuttered side of two bread slices. Top with remaining bread slices, butter side out.
Step 9: Heat a clean skillet over medium heat. Grill sandwiches for 3-4 minutes per side, pressing gently, until bread is golden and cheese is melted.
Step 10: Remove sandwiches from skillet, slice if desired, and serve warm.

Tips & Variations

Use cast iron or a heavy skillet to help achieve even caramelization and browning.
Swap cremini mushrooms for shiitake or portobello for a different flavor.
Add a few slices of cooked bacon or prosciutto for an extra savory touch.
Try a different cheese like Gruyère or fontina for variation.
If you prefer a vegan option, substitute butter with vegan butter and use dairy-free cheese.

Storage

Store any leftover sandwiches wrapped tightly in the refrigerator for up to 2 days. Reheat in a skillet over low heat until warmed through to keep the bread crispy and cheese melty. Avoid microwaving as it can make the bread soggy.

How to Serve

A close-up view of a grilled cheese sandwich with two thick slices of golden brown toasted bread, crispy and sprinkled with herbs and powdered cheese on top, held together by melted white cheese that oozes out generously between the slices. Inside and spilling over the edges are soft, cooked, golden-brown mushroom slices coated in creamy cheese sauce. The sandwich sits on a white plate with some scattered mushrooms and small green herb bits around it, placed on a white marbled surface. photo taken with an iphone --ar 4:5 --v 7

Serve this delicious recipe with your favorite sides.

FAQs

Can I make the caramelized onions ahead of time?

Yes, caramelized onions can be made up to 3 days in advance and stored in an airtight container in the refrigerator. Reheat them gently before assembling the sandwich.

Is the white wine necessary for the mushrooms?

No, the white wine is optional but recommended as it adds depth and brightness to the mushrooms. You can substitute with vegetable broth or simply omit it if preferred.