Introduction

The Swiss Mushroom Melt Sandwich is a comforting and flavorful vegetarian option featuring caramelized onions, sautéed mushrooms, and melted Swiss cheese on crusty sourdough bread. This sandwich combines rich, savory ingredients for a satisfying meal perfect any time of day.

A thick sandwich sits on a white plate with a white marbled surface underneath. The sandwich has two golden-brown toasted bread slices on the top and bottom, each showing a crispy texture with light charring and scattered green herbs. Between the bread layers, melted cheese flows down, creamy white and smooth with a slightly bubbly texture. Under the bottom bread, there is a layer of cooked sliced mushrooms in a glossy brown sauce with sprinkled herbs, some mushrooms spilling out onto the plate. On top of the sandwich, there is a small bunch of fresh curly parsley, bright green and leafy. Photo taken with an iphone --ar 4:5 --v 7

Ingredients

2 large yellow onions, thinly sliced
2 tablespoons olive oil (for onions)
1 tablespoon butter (for onions)
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 (for mushrooms)
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 (for bread)
1 tablespoon Dijon mustard (optional)

Instructions

Step 1: Peel and thinly slice the yellow onions.
Step 2: In a large skillet, heat 2 tablespoons olive oil and 1 tablespoon butter over medium-low heat.
Step 3: Add the sliced onions to the skillet and stir to coat them with the oil and butter.
Step 4: Cook the onions over very low heat, stirring occasionally, for 30-45 minutes until they are deep golden brown and very soft. Reduce heat if they brown too quickly.
Step 5: Stir in the brown sugar and balsamic vinegar. Cook for another 2-3 minutes, stirring constantly, until the sugar dissolves and the balsamic vinegar is absorbed.
Step 6: Season the caramelized onions with salt and freshly ground black pepper to taste. Remove from the skillet and set aside.
Step 7: Clean and slice the cremini mushrooms.
Step 8: In the same skillet, heat 2 tablespoons olive oil over medium-high heat.
Step 9: Add the sliced mushrooms to the skillet and cook, stirring occasionally, until browned and softened, about 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 in the white wine and scrape up any browned bits from the skillet. Let the wine reduce for 1-2 minutes until almost evaporated.
Step 12: Season the sautéed mushrooms with salt and freshly ground black pepper. Remove from the skillet and set aside.
Step 13: Lightly butter one side of each bread slice.
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. Layer half of the Swiss cheese on each slice.
Step 16: On one slice, pile half of the caramelized onions and half of the sautéed mushrooms on top of the cheese. Repeat on the other slice.
Step 17: Cook the sandwiches for 3-5 minutes per side until the cheese melts and the bread is golden and toasted. Cover the skillet with a lid to help the cheese melt faster.
Step 18: Carefully remove the sandwiches from the skillet. Place one slice on top of the other to create a complete sandwich. Cut in half and serve immediately.

Tips & Variations

Use a sharp Swiss cheese or Gruyère for a more pronounced flavor.
For a vegan version, substitute the butter and cheese with plant-based alternatives.
Add a handful of fresh spinach or arugula inside the sandwich for extra freshness and color.
If you don’t have white wine, a splash of vegetable broth works as a substitute when sautéing mushrooms.

Storage

Store leftover sandwiches wrapped tightly in the refrigerator for up to 2 days. To reheat, toast gently in a skillet over low heat until warmed through and the cheese re-melts, or heat in a toaster oven. Avoid microwaving to keep the bread crispy.

How to Serve

A thick toasted sandwich sits on a white plate with a white marbled texture underneath. The sandwich has three main layers: the top and bottom are golden brown, crispy toasted bread with a slightly rough texture. Between the bread layers is a thick, creamy layer of melted cheese that oozes out from the sides, mixed with sautéed light brown mushroom slices that are soft and glossy. The top of the sandwich is sprinkled with finely chopped green herbs and a small bunch of fresh curly parsley sits in the center. Some melted cheese and mushrooms spill onto the plate, adding a rich, gooey look. photo taken with an iphone --ar 4:5 --v 7

Serve this delicious recipe with your favorite sides.

FAQs

Can I use other types of mushrooms?

Yes, cremini mushrooms work well, but you can also use button, shiitake, or portobello mushrooms for different textures and flavors.

Is the white wine necessary?

The white wine adds depth and a subtle acidity to the mushrooms, but you can omit it if you prefer or substitute with vegetable broth for a non-alcoholic option.