This is a black bean and mushroom burger with an In-N-Out-style spread — mayo, ketchup, pickle relish, and smoked paprika — served on a toasted potato bun with lettuce, tomato, and pickles. The honest reason to make it: the sauce takes five minutes and the patties use pantry staples, so the whole thing costs a fraction of a restaurant veggie burger and tastes better than most of them.
Before you start
Two things determine whether these patties hold together or fall apart on the griddle. First, cook the mushrooms long enough that their edges are visibly dry and dark — pull them too early and the residual moisture will make your mix wet and sticky. Second, when you mash the beans, leave roughly a third of them whole. That uneven texture is what gives the patty something to bite into. Skip the egg in the mix — it makes the patty mushy. The beans and breadcrumbs do the binding work here without it. Press each patty to about three-quarters of an inch thick and refrigerate for at least 20 minutes before cooking so they firm up and won’t crack when you flip them.
Make-ahead notes
The sauce keeps in a sealed jar in the fridge for up to two weeks — make a double batch and use it on sandwiches all week. Raw patties can be stacked with parchment between them and refrigerated for up to 24 hours, or frozen for up to two months; freeze them on a flat tray first, then transfer to a bag once solid. Cook from frozen over medium heat with a lid on for the first few minutes to warm the center through before you sear the outside. Cooked patties reheat well in a dry skillet over medium-low for about three minutes per side — the microwave works in a pinch but softens the crust.
Common problems and fixes
- Patties crumble when flipped: The mix is too wet or too loose. Stir in breadcrumbs one tablespoon at a time until the mixture holds its shape when pressed. Panko, crushed crackers, or even rolled oats all work if you’re out of regular breadcrumbs.
- Patties stick to the pan: The pan wasn’t hot enough before you added the patties, or you moved them too soon. Let them cook undisturbed for a full three to four minutes — they’ll release on their own once a crust forms.
- Sauce tastes flat: It needs acid. A small splash of white vinegar or a squeeze of lemon juice sharpens it up immediately. If you’re out of smoked paprika, a pinch of regular paprika plus a drop of hot sauce gets you close.
- Bun goes soggy before you’re halfway through: Spread the sauce on both cut sides of the bun and let it act as a moisture barrier, then put the lettuce directly against the bun rather than next to the patty. Toast the bun a little longer than feels necessary.
- No potato buns available: Brioche buns are the closest swap — soft, slightly sweet, holds up to the sauce. A standard sesame seed bun works fine too; just toast it well so it doesn’t collapse under the toppings.
In-N-Out Veggie Sauce Burger
Ingredients
For the In-N-Out Style Veggie Sauce (Spread):
- 0.5 cup mayonnaise Duke’s recommended for tang
- 3 tbsp ketchup Heinz preferred for consistency
- 2 tbsp sweet pickle relish Bubbies or similar, well-drained
- 1 tsp distilled white vinegar balances richness
- 1 tsp yellow mustard classic diner flavor
- 0.5 tsp granulated sugar rounds acidity
- 0.25 tsp onion powder subtle savoriness
- 0.125 tsp smoked paprika whisper of smokiness
- 1 pinch kosher salt to taste
For the Veggie Patties:
- 1 tbsp extra-virgin olive oil for sautéing mushrooms
- 8 oz cremini mushrooms finely chopped; dry for best sear
- 0.5 cup yellow onion finely minced
- 2 cloves garlic minced
- 0.5 cup walnuts toasted, finely chopped; adds meaty bite
- 15 oz black beans canned, drained and rinsed
- 0.75 cup panko breadcrumbs for structure
- 1 large egg lightly beaten; binder
- 1 tbsp soy sauce or tamari for gluten-free
- 1 tsp vegetarian Worcestershire sauce adds depth
- 1 tsp smoked paprika for subtle smokiness
- 0.5 tsp freshly ground black pepper
- 0.5 tsp kosher salt plus more to taste
For the Burger Build:
- 4 whole soft potato burger buns Martin’s or bakery-soft style
- 2 tbsp unsalted butter softened; for toasting buns
- 2 tbsp neutral oil canola or grapeseed; for searing patties
- 4 slices American cheese optional; classic melt
- 4 leaves iceberg lettuce crisp outer leaves preferred
- 1 large ripe tomato cut into 8 slices
- 8-12 pieces dill pickle chips well-drained
- 1 small yellow onion thinly sliced; optional griddled
Instructions
- Make the Veggie Sauce (Spread): In a small bowl, whisk together mayonnaise, ketchup, sweet pickle relish, white vinegar, yellow mustard, sugar, onion powder, smoked paprika, and a pinch of kosher salt until smooth and peachy-pink.Taste and adjust: you’re looking for a balance of creamy, tangy, and gently sweet. If it tastes flat, add a drop more vinegar; if too tart, a pinch more sugar.Cover and refrigerate for at least 15 minutes to let flavors bloom. The sauce will thicken slightly as it chills.
- Sauté the Mushroom–Onion Base: Set a large skillet over medium-high heat (about 375°F / 190°C). Add olive oil.Add finely chopped mushrooms and cook, stirring occasionally, until they release moisture and turn deep brown with dry edges, 5–6 minutes. You should hear a gentle sizzle, not a wet hiss.Stir in minced onion and cook until translucent and sweet, 2–3 minutes. Add garlic and cook 30 seconds until fragrant. Transfer to a plate to cool slightly, 3 minutes.
- Build the Patty Mixture: In a mixing bowl, lightly mash the black beans with a fork or potato masher, leaving about one-third intact for texture.Add the cooled mushroom–onion mixture, walnuts, panko, beaten egg, soy sauce, vegetarian Worcestershire, smoked paprika, black pepper, and kosher salt.Fold with a spatula until cohesive. If the mix feels loose, sprinkle in another tablespoon of panko. Let the mixture rest 5 minutes so the crumbs hydrate and bind.
- Form the Patties: Divide mixture into 4 equal portions. With damp hands, form 4 round patties about 4 to 4.25 inches wide and 1/2 inch thick. Press a slight dimple in the center to prevent doming.Place patties on a parchment-lined plate and refrigerate while you prep the buns (5 minutes helps them firm).
- Sear the Patties: Heat neutral oil in the skillet over medium-high (surface near 375°F / 190°C). When the oil shimmers, add patties.Sear 3–4 minutes per side until deeply browned and crisp at the edges. Internal temperature should reach at least 165°F / 74°C due to the egg binder.If using cheese, top each patty with a slice during the last 30–60 seconds; cover with a lid to melt.Alternative finish: After a quick sear, transfer patties to a 425°F / 220°C oven for 6–8 minutes to set the center without over-browning.
- Toast the Buns and Onions: Spread butter on cut sides of the buns. Toast cut-side down in the same skillet over medium heat until golden and fragrant, 60–90 seconds.Optional: Add sliced onions to the skillet with a touch of oil and cook 2–3 minutes until lightly charred at the edges and sweet.
- Assemble the In-N-Out Veggie Sauce Burger: Bottom bun: spread 1 tablespoon Veggie Sauce, then add a few pickle chips and a crisp lettuce leaf.Set the hot patty on the lettuce. Spoon 1–2 tablespoons more sauce over the patty.Add 2 tomato slices and some griddled onions (if using). Lightly smear the top bun with sauce and crown the burger.Serve immediately while buns are warm and the patty edges are still crisp.
Notes
Chef’s Tips:
- For Deeper Umami: Add 1 tsp white miso to the patty mix or 1/2 tsp mushroom powder.
- Vegan Adaptation: Replace egg with a flax "egg" (1 tbsp ground flax + 2.5 tbsp water, rested 5 minutes). Use vegan mayo and vegan American-style slices.
- Gluten-free: Use certified gluten-free panko and tamari instead of soy sauce. Select GF buns.
- Faster Caramelized Onions: Add a pinch of baking soda to onions in the pan; it accelerates browning. Stir often and watch closely.
- Texture Control: Don’t over-process mushrooms; fine hand-chopping keeps a pleasant, meaty bite.
- Make-ahead Sauce: The Veggie Sauce improves after 2–24 hours in the fridge.
Serving Suggestions:
Plate on a warmed dish with the burger slightly off-center. Let the lettuce peek out for a bright green rim, the tomato show a glossy red edge, and a touch of sauce kiss the bun. Add a ramekin of extra Veggie Sauce on the side, crisp oven fries, and a cold vanilla shake or sparkling citrus soda. The perfect burger sings with contrast: toasted-golden buns, juicy crimson tomatoes, bright pickles, and the savory aroma of seared mushrooms.Culinary Context:
This burger nods to the West Coast’s legendary drive-thru tradition while bringing a chefly approach to vegetarian cooking. The spread mirrors the beloved thousand-island–style sauce of classic chains, while the patty layers mushrooms, beans, and toasted walnuts for depth and structure—proof that a meatless burger can be indulgent, nostalgic, and truly satisfying.Optional Advanced Instructions:
- Prep Ahead: Mix and shape patties up to 24 hours in advance; keep covered and chilled. Sauce can be made 2 days ahead.
- Batch Cooking: Sear patties, then chill. Reheat in a 400°F / 205°C oven for 8–10 minutes; add cheese in the last minute.
- No Food Processor Needed: Hand-mashing beans and knife-chopping mushrooms preserves texture better than pureeing.
Timing:
- Prep Time: 25 minutes (sauce mixing and chill, sauté base, form patties)
- Cook Time: 15 minutes (sear patties, toast buns, optional onions)
- Total: 40 minutes
Course:
Lunch or DinnerOrigin:
American, Californian (West Coast drive-thru inspiration)Nutrition
FAQ
Can I use canned black beans straight from the can?
Yes, but drain and rinse them thoroughly, then spread them on a paper towel and pat dry before mixing. Excess liquid from the can is one of the main reasons patties fall apart.
What can I use instead of walnuts in the patty?
Sunflower seeds or pepitas work well and are usually cheaper. Roughly chop them to about the same size you’d chop walnuts — you want texture, not a paste.
Can I cook these on an outdoor grill instead of a skillet?
You can, but grill grates are risky with veggie patties — they can stick and break. Oil the grates well, make sure the patties are cold and firm going on, and use a wide spatula. A grill pan on the stovetop is a safer middle ground.
Is there a dairy-free swap for the mayo in the sauce?
Any vegan mayo works as a straight one-for-one replacement and the sauce comes out nearly identical. Plain unsweetened cashew cream is a good homemade option if you have cashews on hand.