These thick, golden Mushroom Patty Melts are stacked with roasted portobello mushrooms, sweet caramelized onions, and melted Swiss cheese tucked between crispy rye bread. I first made this meatless sandwich on a rainy Tuesday when I was craving something warm and satisfying but didn't want anything heavy. The smell of those onions slowly caramelizing filled my whole kitchen, and I knew I'd stumbled onto something special.
If you're looking for other comforting favorites, my Mac and Cheese and Twice Baked Potato Casserole hit that same warm, satisfying spot.
Why You'll Love This Mushroom Patty Melt
It's hearty without the meat. The roasted portobello mushrooms give you that satisfying, meaty bite that makes this sandwich feel like a real meal, not just a snack.
The flavors are rich and balanced. You get the earthy mushrooms, the sweet caramelized onions, the tangy Swiss cheese, and that perfect crispy rye bread all working together.
It's easier than you'd think. Yes, the onions take a bit of time, but they mostly cook themselves. The rest comes together quickly, and the results taste like you spent all day in the kitchen.
Everyone loves it. Whether you're feeding vegetarians or just someone who wants a break from burgers, this portobello Mushroom Patty Melt wins people over every single time.
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Mushroom Patty Melt Ingredients
Here's what you'll need to make these delicious Mushroom Patty Melt.
See Recipe Card Below This Post For Ingredient Quantities
- Vegetable oil (divided)
- Colossal onion, thinly sliced (about 565g or 3 cups)
- Portobello mushrooms
- Garlic cloves, minced (about 1 Tbsp)
- Balsamic vinegar
- Soy sauce
- Dried thyme
- Rye bread
- Mayonnaise
- Swiss cheese
- Salt
- Butter (divided)
How to Make Mushroom Patty Melt
Follow these simple steps to make the best mushroom patty melt you've ever tasted.
Preheat oven: Preheat your oven to 400°F. Get all your ingredients prepped and ready to go so you're not scrambling later.
Caramelize the onions: 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 they're caramelized and golden brown. They'll shrink down quite a bit and smell amazing. Remove from heat, set aside, and wipe out the pan so it's ready for grilling the sandwiches.
Prep the mushrooms: While the onions cook, remove the stems and gills from the portobello mushrooms. Place them cap-side down on a parchment-lined baking sheet.
Make the marinade: In a small bowl, whisk together the minced garlic, balsamic vinegar, remaining ¼ cup vegetable oil, soy sauce, and dried thyme. Pour this mixture over the mushrooms, letting it pool around them. Don't worry if some overflows onto the pan.
Roast the mushrooms: Roast in the oven for 20 minutes until the mushrooms are tender and have soaked up all that flavor. Remove from the oven, let them cool for a few minutes, then slice them into thick pieces.
Assemble the sandwiches: Spread mayo evenly on all 8 slices of rye bread. Top each slice with a piece of Swiss cheese and a generous handful of those sweet caramelized onions.
Add the mushrooms: Place the sliced portobello mushrooms on 4 of the bread slices, sprinkle with a little salt, and top with the remaining bread slices to form 4 sandwiches.
Toast the first batch: In your skillet, melt 1 tablespoon butter over medium heat. Place two sandwiches in the pan and toast for 3 to 4 minutes on each side, until the bread is golden and crispy and the cheese is melted. Add another 1 tablespoon butter when you flip them.
Finish and serve: Repeat with the remaining two sandwiches, using the last 2 tablespoon butter. Serve hot and enjoy every gooey, savory bite.
Smart Substitutions and Variations
Use different cheese: Provolone, Gruyere, or even sharp cheddar work beautifully if you don't have Swiss on hand.
Try sourdough or whole wheat bread: If rye isn't your thing, sourdough gives you a tangy flavor and whole wheat adds a nutty taste.
Make it vegan: Use vegan butter and mayo, and swap the Swiss cheese for your favorite plant-based cheese slices.
Add extra veggies: Sautéed bell peppers or spinach would be a delicious addition tucked in with the mushrooms.
Skip the balsamic: If you don't have balsamic vinegar, red wine vinegar or even a splash of Worcestershire sauce works in a pinch.
Equipment For Mushroom Patty Melt
- Medium skillet: For caramelizing those onions low and slow.
- Parchment-lined baking sheet: Keeps the mushrooms from sticking and makes cleanup easier.
- Small bowl: For whisking together the marinade.
- Skillet for toasting: A good heavy-bottomed skillet gives you even browning on the sandwiches.
Storage and Reheating Tips
Store leftovers: Wrap individual sandwiches tightly in foil or place them in an airtight container. They'll keep in the fridge for up to 2 days.
Reheat in a skillet: Warm them over medium-low heat for a few minutes on each side until the cheese melts again and the bread crisps back up.
Avoid the microwave: It'll make the bread soggy. If you're in a rush, use a toaster oven instead.
Prep ahead: You can roast the mushrooms and caramelize the onions a day in advance. Store them separately in the fridge, then assemble and grill the sandwiches when you're ready to eat.
What to Serve With Your Mushroom Patty Melt
A simple green salad: Something crisp and fresh with a tangy vinaigrette cuts through the richness of the sandwich perfectly.
Sweet potato fries: The sweetness pairs beautifully with the savory mushrooms and onions. My Sweet Potato Black Bean Skillet has similar flavors you might love.
Tomato soup: There's nothing cozier than dipping a warm, cheesy sandwich into a bowl of creamy tomato soup.
Pickles or pickled veggies: A few tangy pickles on the side add a bright, crunchy contrast to every bite.
Expert Tips
Don't rush the onions: Caramelizing takes time, but it's worth it. Keep the heat at medium and stir occasionally. If they start to stick, add a splash of water.
Remove the mushroom gills: They can make the sandwich a little watery and muddy-looking. Just scrape them out gently with a spoon.
Use room temperature butter: It spreads more easily on the bread and helps you get an even, golden crust.
Press the sandwiches gently: Use a spatula to press down on them while they're toasting. It helps the cheese melt faster and everything stick together.
Let them rest for a minute: After you take the sandwiches off the heat, give them a minute to set before slicing. It keeps everything from sliding out.
FAQ
How do I caramelize onions for a patty melt?
Slice them thin and cook them low and slow in a bit of oil over medium heat for about 45 minutes, stirring every now and then. They'll turn golden and sweet. My trick is to keep the heat steady and not try to rush it. If they start sticking, just add a tiny splash of water.
Can I use different types of cheese for a mushroom patty melt?
Absolutely. Provolone, Gruyere, fontina, or even sharp cheddar all melt beautifully and taste delicious. Swiss is classic, but you can't go wrong experimenting with your favorites.
What's the best bread for a mushroom patty melt?
Rye is traditional and has that perfect tangy flavor, but sourdough, whole wheat, or even a hearty white bread work great too. Just pick something sturdy that won't get soggy.
How do I make this mushroom patty melt recipe vegan?
Use vegan butter and mayo, and swap the Swiss cheese for your favorite plant-based cheese. Everything else in the recipe is already plant-based, so it's an easy switch. The roasted mushrooms and caramelized onions still give you all that rich, savory flavor.
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Pairing
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Mushroom Patty Melt
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!
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