This is a copycat of In-N-Out’s off-menu grilled cheese — a soft toasted bun, two slices of melted American cheese, grilled onions, and that tangy Thousand Island-style spread. No meat, no fuss. It’s worth making at home because you can dial in the onion caramelization and spread ratio better than any drive-through window ever will.
Why this recipe works
Two things actually matter here. First, the flat griddle surface — not a pan with high sides — lets moisture escape so the bun toasts instead of steams. A cast-iron skillet or a wide stainless pan works fine; just don’t crowd it. Second, the steam-dome finish: once the cheese is on the bun, a splash of water and a lid traps just enough steam to melt the cheese through without making it greasy or rubbery. Get those two steps right and everything else falls into place.
Smart swaps
- American cheese: This is the right call for melt and flavor. Swap in mild white cheddar if you must, but it won’t get as smooth.
- The spread: Store-bought Thousand Island works in a pinch, but the homemade version in the recipe card is noticeably tangier and worth the two minutes it takes.
- The bun: A standard soft hamburger bun is correct here. A brioche bun is too rich and throws off the balance. Skip anything crusty — it fights the soft-melted-cheese texture you’re going for.
- Onions: Yellow onions are ideal. White onions caramelize faster and can go bitter; sweet onions work but get very soft.
Leftovers and meal prep
The grilled onions and the spread are the real prep wins here. Cook a big batch of onions — they take the most time — and refrigerate them in an airtight container for up to five days. The spread keeps in the fridge for a week. When you want a sandwich, the actual assembly and griddle work takes under five minutes. Fully assembled sandwiches don’t store well; the bun gets soggy fast. If you do have a leftover assembled sandwich, wrap it tightly and refrigerate for up to one day. Reheat it open-faced on a dry skillet over medium-low heat for about three minutes — the microwave turns the bun gummy.
If something goes sideways
- Cheese isn’t melting evenly: Your heat is too high and the bun is browning before the cheese catches up. Drop to medium-low, add the water splash, and cover immediately.
- Bun is soggy on the inside: The griddle wasn’t hot enough before you put the bun down. Let the surface preheat for at least two minutes before toasting.
- Onions are bitter or dry: They cooked too fast over high heat. Caramelizing onions properly takes 15–20 minutes over medium to medium-low — rushing it with high heat just burns the outside.
- Spread tastes flat: It needs more acid. Add a small squeeze of pickle brine or an extra splash of white vinegar and stir before using.
- Everything slides apart when you pick it up: Too much spread, or the onions are too wet. Pat the onions with a paper towel before building, and keep the spread to a thin, even layer on each bun half.
In-N-Out Style Grilled Cheese with Grilled Onions and Signature Spread
Ingredients
For the Signature Spread:
- ⅓ cup mayonnaise Best Foods/Hellmann’s or Duke’s recommended for body
- 2 tablespoons ketchup Heinz or similar
- 1 ½ tablespoons sweet pickle relish drain excess liquid for thicker spread
- 1 teaspoon white distilled vinegar balances richness
- ½ teaspoon granulated sugar optional, for classic thousand-island style sweetness
- ⅛ teaspoon kosher salt fine sea salt also works
For the Grilled Cheese Sandwiches:
- 2 teaspoons neutral oil avocado or canola for high heat
- 2 tablespoons unsalted butter softened; divided use
- 1 medium yellow onion, finely diced about 1 cup diced
- ¼ teaspoon kosher salt for seasoning onions
- 2 whole soft hamburger buns classic enriched or potato buns; split
- 4 slices American cheese deli-style real American; 2 slices per sandwich
- 2 tablespoons water for steam-melting the cheese
- 4 slices ripe tomato 1/4-inch thick
- ⅛ teaspoon freshly ground black pepper for tomato seasoning
- 2 leaves iceberg lettuce crisp outer leaves; cut to bun size
- 6 chips dill pickles optional but classic
- 1 teaspoon yellow mustard optional mustard-grilled bun trick
Instructions
- Make the Signature Spread (5 minutes): In a small bowl, whisk together mayonnaise, ketchup, sweet pickle relish, white vinegar, sugar, and salt until smooth and rosy. Cover and set aside. The flavor blooms if it rests 10 minutes while you prep.
- Prep the Produce (5 minutes): Finely dice the onion (about 1 cup). Slice the tomato into 4 even rounds and season lightly with a pinch of salt and the black pepper. Rinse and dry lettuce leaves; trim to bun size.
- Preheat the Pan: Set a large skillet or flat griddle over medium heat—aim for about 375°F / 190°C. Add 1 tablespoon butter and the oil; when the butter foams and smells nutty, you’re ready to cook.
- Grill the Onions (about 9 minutes): Add diced onion and 1/4 teaspoon kosher salt. Cook, stirring every minute, until soft, translucent, and speckled golden-brown. If browning too quickly, lower the heat slightly; a tablespoon of water can deglaze and keep them tender. You’re looking for sweet aroma and light caramelization—not dark jammy onions.
- Toast the Buns (1–2 minutes): Push onions to one side (or transfer to a warm plate). Spread the remaining 1 tablespoon butter on the cut sides of the buns. Place cut-side down on the skillet until evenly golden at the edges, 1 to 2 minutes. Optional: For the classic “mustard-grilled” note, smear 1/2 teaspoon yellow mustard on each cut side before toasting.
- Melt the Cheese (about 1 minute): Lay 2 slices of American cheese on each bottom bun half. Splash about 1 tablespoon water onto an empty spot on the skillet, cover with a domed lid to trap steam, and melt just until the cheese is glossy and soft, 30 to 60 seconds. Avoid over-melting to keep structure.
- Build the Sandwiches (2 minutes): Spread 1 to 1½ tablespoons of the signature spread on each top bun. On the cheesy bottoms, divide the grilled onions, add 2 tomato slices, pickle chips, and a crisp lettuce leaf. Cap with the dressed top buns.
- Serve Immediately: The ideal bite is hot, drippy, and crisp at the edges. If needed, keep finished sandwiches briefly on a warm tray in a 200°F / 95°C oven while assembling the second one.
- Alternative Method: Toast buns in a 350°F / 175°C oven for 4 to 6 minutes, and melt cheese under a broiler for 20 to 30 seconds, watching closely.
Notes
Chef’s Tips:
- Speed Up Onion Browning: A tiny pinch (less than 1/16 teaspoon) of baking soda encourages faster browning; stir well and don’t overdo it.
- Steam-Dome Melt: A metal mixing bowl makes an excellent dome for quick, even cheese melt.
- Bun Choice: Soft enriched or potato buns best mimic the original; avoid overly crusty bakery rolls.
- Cheese Swap: Real American melts best; for a sharper bite, mix 1 slice American + 1 slice mild cheddar.
- Dietary Tweaks: Use vegan mayo, plant-based American slices, and dairy-free butter for a fully vegetarian/vegan take; choose egg-free buns if needed.
- Mustard-Grilled Variation: Brush a whisper of yellow mustard on the bun before toasting for a tangy sear.
- Even Slicing: Chill tomatoes 10 minutes for cleaner, thinner slices that won’t slide.
- Use soft enriched buns and real American cheese for the most authentic texture. Spread keeps refrigerated up to 5 days.
Nutrition
Common questions
Can I make this on an outdoor grill instead of a stovetop?
Yes, but use a cast-iron griddle plate set over the grates rather than cooking directly on the grill grates. The flat surface is what gives you an even toast on the bun and keeps the cheese from dripping into the fire.
What’s the best way to prep several of these at once for a group?
Pre-cook all the onions and mix the spread ahead of time, then run the buns and cheese through in batches on the griddle just before serving. Keep finished sandwiches warm in a 200°F oven on a wire rack — not a sheet pan — so the bottoms don’t steam and go soft.
Can I freeze the assembled sandwiches?
Freezing assembled isn’t recommended — the lettuce and tomato turn to mush and the bun gets waterlogged on thawing. Freeze only the grilled onions in a zip-lock bag for up to two months, then thaw and reheat in a skillet.
Is there a dairy-free version that still works?
A plant-based American-style slice — the kind sold in individual wrappers — melts reasonably well using the steam-dome method. Avoid shredded dairy-free cheese here; it doesn’t melt smoothly enough for this style of sandwich.
My spread keeps soaking into the bun before I even finish building the sandwich. What am I doing wrong?
The bun is probably still warm when you’re spreading it, which opens up the crumb and lets the sauce absorb straight in. Let the toasted bun cool for 60 seconds before adding the spread, and apply it right before you stack everything.
If you liked this one
- Perfect In-N-Out 2×2 Copycat
- Animal Style Cheeseburger Recipe
- Animal Style Burger Recipe
- Veggie Sauce Burger Perfection