Introduction

The Swiss Mushroom Melt Sandwich is a warm, comforting treat packed with rich caramelized onions, savory sautéed mushrooms, and melted Swiss cheese. Perfect for a cozy lunch or dinner, this sandwich combines hearty flavors and gooey textures that satisfy every bite.

A close-up view of a grilled cheese sandwich with two thick golden brown toasted bread slices, the top slice is crisp and shiny with green herb sprinkles and a small bunch of fresh curly parsley in the center. Between the bread slices is a thick layer of melted cheese that is creamy white and stretchy, dripping down the sides. Under the cheese are sautéed brown mushroom slices, glistening with a light sauce, some spilling onto the white plate around the sandwich. The plate surface has subtle speckles and a white marbled texture background. Photo taken with an iphone --ar 4:5 --v 7

Ingredients

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

Instructions

Step 1: Peel and thinly slice the yellow onions.
Step 2: In a large skillet, heat the olive oil and butter over medium-low heat.
Step 3: Add the sliced onions to the skillet and stir to coat.
Step 4: Cook the onions over very low heat, stirring occasionally, for about 30-45 minutes, or until they are a deep golden brown and very soft. Reduce heat if browning too quickly.
Step 5: Stir in the brown sugar and balsamic vinegar. Cook for another 2-3 minutes, stirring constantly, until the sugar is dissolved and the balsamic is absorbed.
Step 6: Season the caramelized onions with salt and freshly ground black pepper to taste. Remove from skillet and set aside.
Step 7: Clean and slice the cremini mushrooms.
Step 8: In the same skillet, heat the olive oil over medium-high heat.
Step 9: Add the sliced mushrooms to the skillet and cook, stirring occasionally, until they are browned and softened (8-10 minutes). Cook in batches if needed to avoid overcrowding.
Step 10: Add the minced garlic and fresh thyme leaves. Cook for another minute, stirring constantly, until the garlic is fragrant.
Step 11: Pour the white wine into the skillet and scrape up any browned bits from the bottom of the pan. Let the wine reduce for a minute or two until it’s almost completely evaporated.
Step 12: Season the sautéed mushrooms with salt and freshly ground black pepper to taste. Remove from skillet and set aside.
Step 13: Lightly butter one side of each slice of sourdough bread.
Step 14: Spread a thin layer of Dijon mustard on the unbuttered side of two slices of bread.
Step 15: Place the bread slices (buttered side down) in a clean skillet over medium-low heat. On each slice of bread, layer half of the Swiss cheese.
Step 16: On top of the cheese on one slice of bread, pile half of the caramelized onions and half of the sautéed mushrooms. Repeat with the other slice of bread.
Step 17: Cook the sandwiches until the cheese is melted and gooey, and the bread is golden brown and toasted (3-5 minutes per side). Cover the skillet with a lid to help the cheese melt faster.
Step 18: Carefully remove the sandwiches from the skillet. Place one slice of bread on top of the other to create a complete sandwich. Cut in half and serve immediately.

Tips & Variations

Use a mix of mushrooms like shiitake or button mushrooms for varied texture and flavor.
Add a splash of soy sauce to the mushrooms for a deeper umami taste.
Try gruyere or provolone as an alternative to Swiss cheese for a different cheesy twist.
For a vegan option, substitute butter with plant-based margarine and use vegan cheese slices.
Serve with a side of pickles or a simple green salad for a balanced meal.

Storage

Store leftover sandwiches wrapped tightly in plastic wrap or in an airtight container in the refrigerator for up to 2 days. Reheat in a skillet over low heat or in a toaster oven to keep the bread crisp and the cheese melted. Avoid microwaving as it may make the bread soggy.

How to Serve

A white plate holds a sandwich with two thick slices of golden brown toasted bread, crispy and slightly shiny from butter, topped with a small bunch of fresh green parsley. Between the bread slices are creamy melted cheese and sautéed brown mushrooms that spill out at the sides, with the cheese flowing down softly onto the plate mixed with the mushrooms. The top bread has tiny green herb sprinkles and a light dusting of white powder. The scene is set on a white marbled surface with soft warm lighting. 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 and mushrooms ahead of time?

Yes, both caramelized onions and sautéed mushrooms can be prepared up to 2 days in advance and refrigerated in airtight containers. Reheat gently before assembling the sandwich.

What bread works best for this sandwich?

Sourdough is recommended for its sturdy texture and tangy flavor, but any crusty bread like ciabatta or whole wheat works well.