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Caramelized Onion and Mushroom Sourdough Sandwich with Swiss Cheese Recipe

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4.1 from 38 reviews

This ultimate sandwich recipe features deeply caramelized onions, savory sautéed cremini mushrooms with garlic and thyme, and melted Swiss cheese all layered between buttery, toasted sourdough bread. The balance of sweet, earthy, and tangy flavors combined with gooey cheese creates a delicious and satisfying vegetarian sandwich perfect for lunch or dinner.

  • Total Time: 1 hour 5 minutes
  • Yield: 2 sandwiches

Ingredients

Caramelized Onions

  • 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

Sautéed Mushrooms

  • 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
  • Salt and freshly ground black pepper to taste

Sandwich Assembly

  • 4 slices sourdough bread (or your favorite bread)
  • 4 ounces Swiss cheese, thinly sliced
  • 2 tablespoons butter, softened
  • 1 tablespoon Dijon mustard (optional)

Instructions

  1. Prepare Onions: Peel and thinly slice the yellow onions into even slices to ensure uniform caramelization throughout the cooking process.
  2. Heat Oil and Butter for Onions: In a large skillet, combine the olive oil and butter and warm over medium-low heat to create a rich base for softening the onions.
  3. Add Onions to Skillet: Add the sliced onions to the skillet and stir well to coat them evenly in the oil and butter mixture.
  4. Caramelize Onions: Cook the onions slowly over very low heat, stirring occasionally to avoid burning, for approximately 30-45 minutes until they become a deep golden brown and very soft. Adjust the heat down if they start browning too fast.
  5. Enhance Flavor: Stir in the brown sugar and balsamic vinegar, cooking for another 2-3 minutes while stirring constantly until the sugar dissolves and the vinegar is absorbed.
  6. Season Onions: Season with salt and freshly ground black pepper to taste, then remove from the skillet and set aside to cool.
  7. Prepare Mushrooms: Clean and slice cremini mushrooms evenly to ensure uniform cooking.
  8. Heat Oil for Mushrooms: Using the same skillet, heat olive oil over medium-high heat to prepare for sautéing mushrooms.
  9. Sauté Mushrooms: Add the sliced mushrooms to the skillet, cooking in batches if necessary to avoid overcrowding, and stir occasionally until they are browned and softened, about 8-10 minutes.
  10. Add Garlic and Thyme: Stir in minced garlic and fresh thyme leaves, cooking for an additional minute while stirring constantly until the garlic becomes fragrant.
  11. Deglaze with Wine: Pour dry white wine into the skillet, scraping up any browned bits from the bottom for extra flavor, and let the wine reduce until almost completely evaporated.
  12. Season Mushrooms: Season with salt and freshly ground black pepper to taste. Remove from skillet and set aside.
  13. Prepare Bread: Lightly butter one side of each slice of sourdough bread evenly for perfect toasting and flavor.
  14. Spread Mustard: Spread a thin layer of Dijon mustard on the unbuttered side of two slices of bread, adding a tangy complement to the savory fillings.
  15. Assemble Sandwiches: Place the bread slices buttered side down in a clean skillet over medium-low heat. Layer half of the Swiss cheese on each slice of bread.
  16. Add Onions and Mushrooms: On one slice, pile half of the caramelized onions and half of the sautéed mushrooms on top of the cheese. Repeat with the other slice.
  17. Cook Sandwiches: Cook the sandwiches for 3-5 minutes per side, using a lid to cover the skillet which helps melt the cheese completely. Toast until the bread is golden brown and the cheese is melted and gooey.
  18. Finish and Serve: Carefully remove sandwiches from the skillet. Place one slice on top of the other to form a complete sandwich before serving warm.

Notes

  • Cook onions slowly on low heat to develop rich caramelization without burning.
  • Using white wine is optional but adds a great depth of flavor to mushrooms.
  • Butter the bread generously for crisp, golden toasts.
  • Covering the skillet while cooking sandwiches helps cheese melt more evenly.
  • Use fresh thyme for the best aromatic flavor; dried can be substituted but use about one-third the amount.
  • You can substitute Swiss cheese with Gruyère or provolone for a different but complementary taste.
  • Author: Olivia
  • Prep Time: 20 minutes
  • Cook Time: 45 minutes
  • Category: Sandwich
  • Method: Stovetop
  • Cuisine: American
  • Diet: Vegetarian

Find it online: https://yourdailycook.com/caramelized-onion-and-mushroom-sourdough-sandwich-with-swiss-cheese-recipe/