Introduction

The Swiss Mushroom Melt Sandwich is a comforting and savory delight featuring caramelized onions, sautéed mushrooms, and melty Swiss cheese nestled between toasted sourdough slices. This recipe transforms simple ingredients into a satisfying meal perfect for lunch or dinner.

The image shows a thick sandwich with two golden brown toasted bread slices as the top and bottom layers. Inside, there is a rich, light yellow melted cheese layer that oozes and drips down the sides, mixed with sautéed brown mushrooms scattered unevenly throughout the cheese. The sandwich sits on a white plate, with some mushrooms and melted cheese spilled around the base. On top of the sandwich, there is a small bunch of fresh green parsley and finely chopped green herbs sprinkled lightly on the bread. The background features a white marbled texture. 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 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: Season the sautéed mushrooms with salt and freshly ground black pepper to taste. Remove from skillet and set aside.
Step 12: Lightly butter one side of each slice of sourdough bread.
Step 13: Spread a thin layer of Dijon mustard on the unbuttered side of two slices of bread.
Step 14: 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 15: 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 16: 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 17: 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 richer flavor, try adding a splash of white wine when sautéing the mushrooms.
Swap Swiss cheese for Gruyère or mozzarella for a different cheesy twist.
Use whole grain or rye bread for added texture and nutrition.
Add fresh spinach or arugula inside the sandwich for a fresh, peppery bite.

Storage

Store any leftover sandwiches wrapped tightly in the refrigerator for up to 2 days. Reheat gently in a skillet over low heat or in a toaster oven to keep the bread crisp and the cheese melty. Avoid microwaving to prevent sogginess.

How to Serve

A close-up of a sandwich on a white plate with a white marbled surface, showing three main layers: the bottom layer is a thick, soft bread bun with a light golden crust, spread with a thin layer of white sauce; above it is a juicy, cooked beef patty topped with two slices of melted pale yellow cheese; the top layer has a generous pile of cooked dark brown mushrooms and translucent sautéed onions, with some onions spilling onto the plate, and the top half of the bread bun resting behind. 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 substitute with button mushrooms, portobello, or shiitake for varied flavors and textures.

Is Dijon mustard necessary?

No, the Dijon mustard is optional but it adds a nice tangy contrast to the rich mushrooms and cheese. You can omit it if you prefer a milder flavor.