Introduction

The Swiss Mushroom Melt Sandwich is a comforting and flavorful delight featuring sweet caramelized onions, savory sautéed mushrooms, and melted Swiss cheese. Perfect for a cozy lunch or dinner, this sandwich brings together rich textures and deep, satisfying flavors.

A grilled sandwich with two thick, crispy golden-brown bread slices forms the top and bottom layers. Between them is a thick layer of melted cheese oozing out, covering sautéed mushroom slices that spill out on one side of the sandwich and onto a white speckled plate. The sandwich is garnished with chopped green herbs and topped with a small bunch of fresh curly parsley. The dish sits on a white marbled surface with warm lighting highlighting the textures and colors. 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
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 with the oil and butter.
Step 4: Cook the onions over very low heat, stirring occasionally, for about 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 is dissolved and the 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 and cook, stirring occasionally, until browned and softened, about 8-10 minutes. Cook in batches if needed to avoid overcrowding.
Step 10: Add 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 browned bits from the pan. Let it reduce for 1-2 minutes until almost evaporated.
Step 12: Season the 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 (if using) on the unbuttered side of two slices of bread.
Step 15: Place the bread slices butter side down in a clean skillet over medium-low heat. Layer half of the Swiss cheese on each slice of bread.
Step 16: On top of the cheese on one slice, pile half of the caramelized onions and half of the sautéed mushrooms. Repeat on the other bread slice.
Step 17: Cook the sandwiches until the cheese melts and bread is golden brown and toasted, about 3-5 minutes per side. Cover the skillet with a lid to help cheese melt faster.
Step 18: Carefully remove the sandwiches, place one piece of bread on top of the other to form a complete sandwich. Cut in half and serve immediately.

Tips & Variations

Use other types of mushrooms like shiitake or portobello for a different flavor profile.
Adding a handful of fresh spinach or arugula inside the sandwich adds a nice fresh contrast.
For a vegan version, substitute Swiss cheese with a plant-based cheese and use olive oil or vegan butter instead of dairy butter.
Cooking the onions low and slow is key to developing their natural sweetness and depth of flavor.

Storage

Store leftover sandwiches wrapped in foil or airtight containers in the refrigerator for up to 2 days. Reheat gently in a skillet over low heat to maintain the crispness of the bread and melt the cheese without drying out the filling.

How to Serve

A thick sandwich features two golden brown toasted bread slices with a crispy texture on top and bottom layers. Between the slices, there is a thick layer of melted white cheese that oozes out, mixed with cooked brown mushroom slices scattered generously inside and around the sandwich on a white plate with some green herbs sprinkled on top of the sandwich. The top slice of bread is garnished with a small bunch of fresh green parsley, adding a splash of color. The setting is 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 can be prepared a day or two in advance and stored separately in airtight containers in the refrigerator. Reheat them gently before assembling the sandwich.

What type of bread works best for this sandwich?

Sourdough is ideal because it toasts well and has a sturdy texture to hold the fillings, but you can also use other crusty breads like ciabatta or a hearty whole grain loaf.