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Swiss Mushroom Melt Sandwich

Swiss mushroom melt sandwich with caramelized onions and melted cheese on sourdough bread
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Toasted sourdough sandwich filled with caramelized onions, sautéed mushrooms, and melted Swiss cheese. Perfect for lunch or dinner.

Ingredients

Scale
  • 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)
  • 1 tablespoon fresh thyme leaves
  • 4 slices sourdough bread
  • 4 ounces Swiss cheese, thinly sliced
  • 2 tablespoons butter, softened
  • 1 tablespoon Dijon mustard (optional)

Instructions

  1. Heat olive oil and butter in a large skillet over medium-low heat. Add sliced onions and cook over low heat for 30-45 minutes, stirring occasionally, until deep golden brown and very soft.
  2. Stir in brown sugar and balsamic vinegar into caramelized onions. Cook for 2-3 minutes, stirring constantly, until sugar dissolves. Season with salt and pepper. Remove and set aside.
  3. In the same skillet, heat olive oil over medium-high heat. Add sliced mushrooms and cook for 8-10 minutes, stirring occasionally, until browned and softened.
  4. Add minced garlic and fresh thyme to mushrooms. Cook for 1 minute, stirring constantly. If using wine, pour into skillet and let reduce for 1-2 minutes. Season with salt and pepper. Remove and set aside.
  5. Butter one side of each bread slice. Optional: spread Dijon mustard on unbuttered side. Place bread buttered-side-down in clean skillet over medium-low heat. Layer Swiss cheese on each slice, then add onions and mushrooms to two slices.
  6. Cook for 3-5 minutes until cheese melts and bread turns golden brown. Cover skillet with lid to help cheese melt. Flip plain cheese slices onto loaded slices to create complete sandwiches. Cook 2-3 minutes more until both sides are golden.
  7. Remove from heat, cut sandwiches in half, and serve immediately while hot and cheese is melted.

Notes

  • Don’t rush the caramelized onions. Low and slow cooking develops sweetness and depth of flavor.
  • Wipe mushrooms clean with damp paper towel instead of washing to prevent waterlogging.
  • Cover skillet with lid while cooking to help cheese melt faster and more evenly.
  • Gruyere, provolone, or sharp cheddar can substitute for Swiss cheese.

Nutrition

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