I LOVE ANYTHING MUSHROOM! Clearly, I was excited to create this riff on a classic patty melt, but with a twist. You won’t find any meat here, but instead a budget-friendly and satisfying melt stacked with mushrooms and packed with all the flavors. These Mushroom Patty Melt sandwiches still retain the essence of a classic patty melt, keeping the rye bread, caramelized onions, and Swiss cheese. The mushrooms, however, are roasted with garlic, thyme, balsamic vinegar, and soy sauce, which makes them irresistible. I can’t wait for you to try it and share my passion for the portobello!
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Easy Mushroom Patty Melt Recipe
These meatless portobello patty melts still deliver all the rich, diner-style comfort I’ve always loved in a traditional melt. The rye bread gets crisp and golden in the skillet, the Swiss cheese turns gooey, and the sweet caramelized onions tie everything together. Instead of a beef patty, I use roasted portobello mushrooms, which soak up the homemade garlicky balsamic-soy marinade and bring deep, savory flavor to every bite. Patty melts have been a staple on American diner menus for decades now, and this version keeps that old-school charm while giving it a modern, veggie-forward twist.
Mushroom Patty Melt
Servings 4 sandwichesIngredients
- ½ cup vegetable oil (divided, $0.33)
- 1 colossal onion (thinly sliced (565g, about 3 cups) $0.93*)
- 4 large portobello mushrooms ($5.36)
- 2 garlic cloves (minced, (1 Tbsp) $0.12)
- ¼ cup balsamic vinegar ($0.48)
- ⅛ cup soy sauce ($0.11)
- ½ tsp dried thyme ($0.22)
- 8 slices rye bread ($1.37)
- ⅓ cup mayonnaise ($0.30**)
- 8 slices Swiss cheese ($1.31**)
- ¼ tsp salt ($0.01)
- 4 Tbsp butter (divided, $0.50***)
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, then wipe out the pan for the sandwiches.
- 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 on the mushroom caps. It’s ok if it overflows. Roast the mushrooms in the oven for 20 minutes, then set aside. 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 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.
- To cook the patty melts, melt 1 Tbsp butter in the skillet over medium heat. Place two sandwiches in the skillet. Toast for 3–4 minutes, then add another Tbsp 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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Equipment
- Small Bowl
- Medium Skillet
- 10×15'' Baking Sheet
- Parchment Paper
Notes
Nutrition
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Gather all of your ingredients and preheat your oven to 400°F.
Caramelize the onions: Warm ¼ cup vegetable oil in a medium-sized skillet over medium heat. Add 1 sliced colossal onion (or two smaller onions totalling about 3 cups once sliced) and cook for about 45 minutes. Stir the onions occasionally until they become caramelized and golden. Making caramelized onions is a labor of love, but the results are worth it, so it pays to be patient! See our guide on how to make caramelized onions for more tips and tricks.
Once done, remove the onions and set them aside. Wipe down the pan for the sandwiches.
Clean the mushrooms: While your onions are caramelizing, use a spoon to scoop out the stems and gills from 4 portobello mushrooms. If they’re quite dirty, you can also wipe them down with a damp paper towel. Place the cleaned mushrooms cap side down on a parchment-lined baking sheet.
Make the marinade: Whisk together 2 minced garlic cloves, ¼ cup balsamic vinegar, remaining ¼ cup vegetable oil, ⅛ cup soy sauce, and ½ tsp dried thyme in a small bowl.
Roast the mushrooms: Now, carefully spoon the marinade into the prepared mushroom caps. It’s ok if they overflow a bit!
Roast the mushrooms in your preheated oven for 20 minutes. Set them aside to cool.
Slice the mushrooms: Once they’re cool enough to handle, slice the mushrooms into strips.
Assemble the sandwiches: Lay out 8 slices of rye bread and spread mayo evenly on each slice, using ⅓ cup of mayo total. Top the slices with Swiss cheese (8 slices) and the caramelized onions. Add the sliced portobello mushrooms to 4 slices of bread and sprinkle with ¼ tsp salt, then top with the remaining 4 slices to form sandwiches.
Cook: Melt 1 Tbsp of butter in your skillet over medium heat. Place two sandwiches into the skillet and toast for 3-4 minutes. Then, add another Tbsp of butter, carefully flip the sandwiches, and toast for 3-4 minutes on the other side. Depending on the size of your skillet and how many sandwiches it can fit, you may need to cook in more than two batches.
Repeat the cooking process with the remaining sandwiches and butter. Serve and enjoy!
Recipe Success Tips & Suggestions
- Avoid washing mushrooms directly in water, as they can become mushy. Instead, I recommend wiping them with a damp paper towel to remove dirt, if needed.
- I like to remove the stems since they can be a bit tough, and then gently scrape out the gills with a spoon. They tend to add a slightly bitter, muddy flavor that I’d rather leave out.
- You can customize this vegetarian patty melt with different breads, cheese, and fillings. I’ve used sourdough and regular sandwich bread before. Mozzarella melts beautifully and gives it a mild, creamy flavor, but sharp cheddar or provolone are great, too. I sometimes tuck in a few tomato slices or even some sautéed spinach. I bet sauerkraut, as used in a classic Reuben sandwich, would also be delicious.
- Mushrooms soak up flavor like a sponge, so even a simple marinade made with different spices, herbs, and vinegars will taste great. Try adding ½ to 1 Tbsp brown sugar, like in the marinade for our one-pan mushroom steak dinner, or use the marinade from our portobello mushroom burgers instead!
How to Serve Mushroom Patty Melt Sandwiches
I almost always pair this patty melt with fries. It just hits that classic diner-style combo I grew up loving. Air fryer French fries are perfectly crispy and way easier to make than the deep-fried kind. If I want something fresh to balance the richness, I’ll go for our Mediterranean coleslaw or a simple Greek salad. Of course, these easy mushroom Swiss patty melts are just as delicious on their own or with your favorite chips on the side!
Storage, Meal Prep & Reheating
These easy mushroom patty melts will keep in the fridge for up to 5 days. You can enjoy them cold, but I like reheating them in a skillet with a little extra butter to get the bread crispy again.
If you’re planning ahead, you can prep the mushrooms and caramelized onions in advance, store them separately, and just assemble and toast the sandwiches when you’re ready to eat. The cooked mushrooms, caramelized onions, and untoasted rye bread also freeze well for 3-6 months. Just thaw everything in the fridge overnight before building and toasting your melts.
I saw this and had to make it immediately. Holy amazing. The flavor is incredible. Another bb lunch favorite 😍
Recipe turned out fine. An hour and 15 min for a sandwich is a bit fussy for my tastes. When Beth ran the site, she realized that “budget” also meant time — the most valuable thing we have.
Hi Ivy, time is certainly a valuable resource, and we always aim to balance cost, flavor, and effort in our recipes. That said, even when Beth was running the site, she created many recipes that took time — including ones that featured slow-simmered sauces, braised dishes, and yes, even caramelized onions (which, in this case, are the component that adds to the prep time of this recipe). Sometimes, a little extra effort brings big flavor payoff, but we know it’s not for everyone, and that’s okay!
We also want to gently note that Beth did occasionally work with sponsors as well. Our team continues to carry on her mission of making delicious food accessible and affordable, and for many of our readers, partnerships like the one we did recently have provided real value.
Even if this particular recipe isn’t your style, or you don’t want to spend your hard-earned dollars a specific product or service we recommend, we hope you’ll continue to find recipes here that do fit your needs. Thanks for being part of the Budget Bytes community.
You can wash mushrooms in water