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A close-up of a delicious Mushroom Patty Melt sandwich, featuring golden toasted bread, melted cheese, and sautéed mushrooms, served with crispy fries and pickles.

Mushroom Patty Melt

A comforting meatless delight with roasted portobello mushrooms, Swiss cheese, and caramelized onions.
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Course: Main Course
Cuisine: American
Keyword: meatless sandwich, mushroom melt, Mushroom Patty Melt, patty melt, portobello sandwich
Prep Time: 15 minutes
Cook Time: 1 hour
Total Time: 1 hour 15 minutes
Servings: 4
Calories: 864kcal
Cost: $11

Ingredients

  • ½ cup vegetable oil divided
  • 1 colossal onion thinly sliced; about 3 cups
  • 4 large portobello mushrooms stems and gills removed
  • 2 garlic cloves minced
  • ¼ cup balsamic vinegar
  • ⅛ cup soy sauce
  • ½ teaspoon dried thyme
  • 8 slices rye bread
  • ⅓ cup mayonnaise
  • 8 slices Swiss cheese
  • ¼ teaspoon salt
  • 4 tablespoon butter divided

Instructions

  • Preheat the oven to 400°F. Gather and prepare all ingredients.
  • In a medium skillet over medium heat, warm ¼ cup vegetable oil. Add the sliced onions and cook, stirring occasionally, for about 45 minutes until caramelized and golden. Remove and set aside.
  • While the onions are cooking, remove the stems and gills from the mushrooms and place them, cap side down, on a parchment-lined sheet tray.
  • In a small bowl, whisk together the garlic, balsamic vinegar, remaining ¼ cup vegetable oil, soy sauce, and thyme. Carefully pour this mixture over the mushroom caps. It’s okay if it overflows.
  • Roast the mushrooms in the oven for 20 minutes, then remove and let them cool. Once cooled, slice the mushrooms.
  • To assemble the patty melts, lay out the rye bread and spread mayo evenly over all 8 slices. Top each slice with Swiss cheese and caramelized onions. Add the sliced portobello mushrooms to 4 slices of bread and sprinkle with salt, then close with the remaining 4 slices to form sandwiches.
  • Melt 1 tablespoon butter in the skillet over medium heat. Place two sandwiches in the skillet. Toast for 3–4 minutes, then add another tablespoon of butter, carefully flip, and cook for 3-4 more minutes. Repeat with the remaining two sandwiches and butter.
  • Serve and enjoy!

Notes

For a vegan version, swap the mayo, cheese, and butter with plant-based alternatives. You can also use oil to toast the sandwiches instead of butter.

Nutrition

Serving: 1Serving | Calories: 864kcal | Carbohydrates: 52g | Protein: 19g | Fat: 66g | Sodium: 1225mg | Fiber: 7g