Introduction

The Swiss Mushroom Melt Sandwich is a savory delight that combines caramelized onions, sautéed mushrooms, and melted Swiss cheese on toasted sourdough bread. This recipe is perfect for a cozy lunch or a satisfying dinner that’s full of rich, comforting flavors.

A grilled sandwich sits in the center of a white plate with three visible layers: the top layer is a golden-brown toasted bread slice with a crispy texture, sprinkled with herbs and topped with a small bunch of fresh green parsley. The middle layer features warm, melted cheese dripping down the sides, showing a smooth, creamy texture. The bottom layer has sautéed mushrooms in light brown sauce, spread beneath the cheese with visible slices and a glossy finish, some spilling onto the plate around the sandwich. The whole dish is set against a white marbled surface, with a fork on the bottom left side. 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
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

For a vegan version, substitute the Swiss cheese with your favorite plant-based cheese and use vegan butter or olive oil.
If you don’t have dry white wine, replace it with vegetable broth or skip it altogether, though the wine adds a nice depth of flavor.
Try adding a handful of fresh spinach or arugula inside the sandwich for a fresh, peppery contrast.
Use rye or whole-grain bread for a different flavor profile.

Storage

Store leftover sandwiches wrapped tightly in foil or airtight containers in the refrigerator for up to 2 days. To reheat, warm them in a skillet over medium heat until the cheese is melted and the bread is crisp again. Avoid microwaving to keep the bread from becoming soggy.

How to Serve

A thick sandwich sits on a white plate with one slice of golden-brown toasted bread on top, sprinkled with a light dusting of white powder and small green herbs, crowned with a small bunch of fresh parsley. Underneath, a layer of gooey melted cheese drips down the sides, mixed with sautéed brown mushrooms. The sandwich’s bottom layer is another slice of toasted bread, visible beneath the cheese and mushrooms. Some mushrooms and bits of cheese spill onto the plate around the sandwich. The entire scene rests on a white marbled background. 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 sautéed mushrooms ahead of time?

Yes, you can prepare both components a day ahead and store them separately in airtight containers in the fridge. Reheat gently before assembling the sandwiches.

What type of cheese works best in this sandwich?

Swiss cheese is traditional for its mild, nutty flavor and excellent melting quality, but Gruyère or mozzarella can also be delicious alternatives.