This Mushroom Patty Melt is loaded with roasted portobello mushrooms, sweet caramelized onions, and gooey melted Swiss cheese, all pressed between buttery, golden rye bread. I started making these when I wanted a vegetarian sandwich that felt just as hearty and satisfying as a traditional patty melt, and the combination of meaty portobellos with the sweet onions and nutty Swiss cheese turned out to be absolutely perfect. The mushrooms get marinated in balsamic vinegar, garlic, and soy sauce, then roasted until they're tender and packed with flavor.
If you love hearty, satisfying meals, you'll also want to try my Beef Enchiladas, Sweet Potato and Chickpea Curry, and for something creamy, my One Pot Mac and Cheese.
Why You'll Love This Mushroom Patty Melt
Hearty and satisfying. The portobello mushrooms are meaty and filling, making this sandwich substantial enough for lunch or dinner.
Packed with flavor. The balsamic marinade, caramelized onions, and Swiss cheese create layers of sweet, savory, and tangy flavors.
Vegetarian comfort food. This is the kind of sandwich that satisfies meat-eaters and vegetarians alike. It's rich, indulgent, and comforting.
Golden and crispy. Griddling the sandwich in butter creates a crispy, golden crust that contrasts perfectly with the gooey melted cheese.
Great for meal prep. You can caramelize the onions and roast the mushrooms ahead of time, then assemble and cook the sandwiches when you're ready to eat.
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Mushroom Patty Melt ingrediants
Here's everything you need to make this hearty, flavorful Mushroom Patty Melt.
See Recipe Card Below This Post For Ingredient Quantities
Vegetables & Mushrooms:
- Colossal onion: Thinly sliced and caramelized low and slow until golden and sweet. The onions add a deep, sweet flavor that balances the savory mushrooms.
- Large portobello mushrooms: The "patty" in this patty melt. Portobellos are meaty, substantial, and full of umami flavor. Removing the gills keeps them from turning the sandwich dark.
Sauce & Seasoning:
- Garlic cloves: Minced garlic adds a savory, aromatic depth to the mushroom marinade.
- Balsamic vinegar: Adds a tangy sweetness that enhances the mushrooms and balances the richness of the cheese.
- Soy sauce: Brings umami and a salty depth that makes the mushrooms taste even meatier.
- Dried thyme: Adds an earthy, herby flavor that complements the mushrooms.
- Salt: Seasons the mushrooms and brings out all the other flavors.
Bread & Cheese:
- Rye bread: Traditional for patty melts. Rye has a slightly tangy, nutty flavor that pairs perfectly with Swiss cheese and caramelized onions.
- Swiss cheese: Melts beautifully and has a mild, nutty flavor that complements the mushrooms without overpowering them.
- Mayonnaise: Spread on the bread before griddling. It helps the bread get golden and crispy and adds a subtle richness.
Cooking Fats:
- Vegetable oil: Used for caramelizing the onions and marinating the mushrooms.
- Butter: Used for griddling the sandwiches. Butter creates a golden, crispy crust and adds rich flavor.
How to Make Mushroom Patty Melt
- Preheat oven: Set your oven to 400°F (200°C) and prepare all your ingredients. This makes the cooking process smoother.
- Caramelize onions: Heat ¼ cup of vegetable oil in a medium skillet over medium heat. Add the thinly sliced onions and cook, stirring occasionally, for about 45 minutes until they're golden brown and caramelized. The onions will shrink down significantly and turn sweet and soft. Remove them from the skillet and set aside.
- Prepare mushrooms: Remove the stems from the portobello mushrooms and use a spoon to scrape out the dark gills. This prevents the mushrooms from turning everything dark and keeps the texture better. Place the mushroom caps, cap side down, on a parchment-lined baking sheet.
- Make mushroom marinade: In a small bowl, whisk together the minced garlic, balsamic vinegar, remaining ¼ cup vegetable oil, soy sauce, and dried thyme. Pour this marinade over the mushroom caps, making sure they're well coated. Roast the mushrooms in the preheated oven for 20 minutes until they're tender and have absorbed the marinade. Once they're cool enough to handle, slice the mushrooms into strips.
- Assemble sandwiches: Spread the mayonnaise evenly over all 8 slices of rye bread. Place a slice of Swiss cheese on each piece of bread. Divide the caramelized onions evenly among all 8 slices. On 4 of the slices, add the sliced roasted mushrooms and sprinkle with a pinch of salt.
- Cook patty melts: Melt 1 tablespoon of butter in the skillet over medium heat. Place two sandwiches in the pan and cook for 3 to 4 minutes until the bottom is golden and crispy. Add another tablespoon of butter to the pan, then carefully flip the sandwiches and cook for another 3 to 4 minutes until the second side is golden and the cheese is melted.
- Serve: Slice the sandwiches in half if desired and serve them warm. The cheese should be gooey and melted, and the bread should be golden and crispy.
Substitutions and Variations
Different cheese: Use provolone, cheddar, or Gruyere instead of Swiss for different flavors.
Add bacon: For a non-vegetarian version, add crispy bacon slices to the sandwiches.
Different bread: Use sourdough, whole wheat, or pumpernickel if you don't have rye bread.
Add greens: Tuck in some arugula or spinach for extra freshness and nutrition.
Spicy version: Add sliced jalapeños or a few dashes of hot sauce to the mushrooms.
Make it vegan: Use vegan cheese and vegan butter, and replace the mayo with vegan mayo.
Equipment
Oven: For roasting the marinated portobello mushrooms.
Baking sheet: For roasting the mushrooms. Line it with parchment paper to prevent sticking.
Parchment paper: Keeps the mushrooms from sticking to the baking sheet.
Medium skillet: For caramelizing the onions and griddling the sandwiches.
Small bowl for marinade: For whisking together the mushroom marinade ingredients.
Whisk: For mixing the marinade until smooth.
Knife for slicing: For slicing the onions and mushrooms.
Spoon or spatula: For spreading the mayonnaise on the bread and flipping the sandwiches.
Storage and Reheating Tips
Refrigerator: Store leftover sandwiches wrapped in foil or in an airtight container in the fridge for up to 2 days.
Freezing: You can freeze the roasted mushrooms and caramelized onions separately for up to 3 months. Thaw in the fridge before assembling the sandwiches.
Reheating: Reheat the sandwiches in a skillet over medium heat for 2 to 3 minutes per side until warmed through and crispy. You can also reheat them in the oven at 350°F for 10 minutes.
Make ahead: Caramelize the onions and roast the mushrooms up to 2 days ahead. Store them separately in the fridge, then assemble and cook the sandwiches when you're ready to eat.
Serving Suggestions
With a side salad: Serve the patty melt with a crisp green salad dressed with a light vinaigrette.
With fries or chips: Classic diner style. Serve with french fries, sweet potato fries, or kettle chips.
With pickles: Add some dill pickles on the side for a tangy crunch that cuts through the richness of the sandwich.
With tomato soup: A bowl of warm tomato soup pairs perfectly with this cheesy, crispy sandwich.
Expert Tips
Remove the mushroom gills. The dark gills can make the sandwich look muddy and can add a slightly bitter flavor. Scraping them out with a spoon takes just a minute and makes a big difference.
Let the mushrooms cool before slicing. Hot mushrooms are slippery and hard to slice evenly. Let them cool for a few minutes first.
Use plenty of butter. Don't skimp on the butter when griddling the sandwiches. It's what creates that golden, crispy crust.
Press the sandwiches gently. Use a spatula to press down gently on the sandwiches while they cook. This helps the cheese melt and the bread get crispy and golden.
Watch the heat. Medium heat is key. Too high and the bread will burn before the cheese melts. Too low and the sandwich won't get crispy.perature, but they should still be juicy for best results.
FAQ
Traditional patty melt sauce is usually a combination of mayonnaise, ketchup, and sometimes a little mustard or pickle relish, similar to Thousand Island dressing or special sauce. In this mushroom patty melt, the sauce is simply mayonnaise spread on the bread, which gets golden and crispy when griddled. You can also add ketchup, mustard, or horseradish to the mayo if you want more flavor.
To make a Mushroom Patty Melt, marinate and roast portobello mushrooms until they're tender and flavorful. Caramelize onions low and slow until they're golden and sweet. Spread mayo on rye bread, add Swiss cheese, caramelized onions, and sliced mushrooms, then top with another slice of bread. Griddle the sandwiches in butter over medium heat until the bread is golden and crispy and the cheese is melted. The key is using hearty portobello mushrooms that can stand in for a beef patty.
The main differences are the bread and the cooking method. A burger is typically served on a soft bun and can be grilled or pan-fried. A patty melt is always made on sliced bread, usually rye, and is griddled like a grilled cheese sandwich with butter until the bread is crispy and golden. Patty melts also traditionally have caramelized onions and Swiss cheese, while burgers can have a variety of toppings and cheese.
A Mushroom Patty Melt is a classic American diner sandwich that combines elements of a burger and a grilled cheese. It's traditionally made with a beef patty, caramelized onions, and Swiss cheese on rye bread, griddled in butter until the bread is golden and crispy and the cheese is melted. This mushroom version replaces the beef patty with marinated, roasted portobello mushrooms for a hearty vegetarian alternative that's just as satisfying.
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Pairing
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Mushroom Patty Melt
Ingredients
Method
- Preheat the oven to 400°F (200°C) and gather 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 golden and caramelized. Remove and set aside, then wipe out the skillet.
- Remove the stems and gills from mushrooms and place caps, cap side down, on a parchment-lined baking sheet.
- In a small bowl, whisk together garlic, balsamic vinegar, remaining ¼ cup vegetable oil, soy sauce, and thyme. Pour over mushroom caps and roast in the oven for 20 minutes. Allow to cool slightly, then slice.
- Spread mayonnaise evenly over all 8 slices of rye bread.
- Top each slice with Swiss cheese and caramelized onions. Add sliced mushrooms to 4 slices, sprinkle with salt, then close sandwiches with the remaining bread slices.
- Melt 1 tablespoon butter in the skillet over medium heat. Toast two sandwiches for 3–4 minutes, add another 1 tablespoon butter, flip carefully, and cook 3–4 more minutes. Repeat with the remaining sandwiches.
- Serve immediately and enjoy.
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