In-N-Out Flying Dutchman Copycat with Grilled Onions

Why You’ll Love This Recipe

• Faithful copycat of the iconic mustard-seared, cheese-stacked Flying Dutchman—no bun required.
• Fast and simple: pantry mustard, American cheese, and a quick house spread deliver big flavor.
• Golden, diner-style grilled onions bring sweetness that balances the savory crust.
• Low-carb friendly and easy to scale for a crowd.

Grocery List

• Produce: 1 large yellow onion
• Dairy: American cheese slices (4)
• Pantry: 80/20 ground beef (8 oz), yellow mustard, mayonnaise, ketchup, sweet pickle relish, white vinegar, sugar, kosher salt, black pepper, neutral oil

Full Ingredients

For the mustard-smashed patties

• 8 oz (225 g) 80/20 ground beef, divided into 4 balls (2 oz each)
• 3/4 tsp kosher salt
• 1/2 tsp freshly ground black pepper
• 4 tsp classic yellow mustard (1 tsp per patty)
• 1 tsp neutral oil (canola, avocado, or grapeseed) for the skillet
• 4 slices American cheese (about 0.7 oz each)

For the grilled onions

• 1 large yellow onion, finely diced (about 2 cups)
• 2 tsp neutral oil
• Pinch of kosher salt
• 2 tbsp water, for deglazing/steaming

For the spread (makes about 1/2 cup)

• 1/4 cup mayonnaise
• 2 tbsp ketchup
• 2 tbsp sweet pickle relish
• 1 tsp white distilled vinegar
• 1/2 tsp granulated sugar
• Pinch kosher salt

For serving

• Grilled onions (from above)
• Spread (on the side)

Step-by-Step Instructions

Step 1: Make the spread

In a small bowl, whisk together the mayonnaise, ketchup, sweet pickle relish, white vinegar, sugar, and a pinch of salt until smooth and evenly pink. Cover and refrigerate so the flavors meld while you cook (at least 10 minutes).

Step 2: Cook the grilled onions

Heat 2 tsp neutral oil in a medium skillet over medium heat. Add the finely diced onion and a pinch of salt. Cook, stirring occasionally, until translucent and lightly golden, 6–8 minutes. Add 2 tbsp water and continue cooking, stirring, until the water evaporates and onions are soft, jammy, and deep golden, 3–4 minutes more. Keep warm on low or rewarm before serving.

Step 3: Preheat the pan and portion the beef

Place a heavy cast-iron or stainless steel skillet over medium-high heat for 2–3 minutes, aiming for a surface temperature of about 425–450°F. Lightly film with 1 tsp neutral oil. While it heats, divide the beef into four 2 oz balls and season the exteriors with the kosher salt and black pepper.

Step 4: Smash the patties

Set two beef balls in the hot skillet, leaving space between them. Immediately cover each with a small square of parchment and press firmly with a stiff spatula or burger press to 1/8–1/4 inch thickness. Remove the parchment. Do not move the patties. Sear until the edges are deeply browned and lacy, 45–60 seconds.

Step 5: Mustard-sear, flip, and cheese

Brush the uncooked tops of the patties with 1 tsp yellow mustard each. Flip so the mustard sides contact the pan; the mustard will sizzle and caramelize, adding tang and color. Place one slice of American cheese on each of two patties. Cook 30–45 seconds more, until the cheese melts and the patties are cooked through (ground beef should reach 160°F). Transfer to a tray and repeat with the remaining two patties.

Step 6: Stack and serve

Build each Flying Dutchman by placing a cheese-topped patty on the plate, then stacking a plain patty over it so two slices of American cheese are sandwiched between the two patties. Serve immediately, bunless, with a generous spoonful of grilled onions on the side and a ramekin of spread for dipping or spooning over.

Pro Tips

• Cold meat, hot pan: Keep beef chilled until the moment you smash for the crispiest crust.
• Use parchment to prevent sticking: A 4-inch square makes it easy to press ultra-thin without tearing.
• Do not overwork the meat: Loosely formed balls lead to better craggy edges and a superior sear.
• Mustard timing matters: Brush mustard on the top side just before flipping so it caramelizes against the pan.
• Cover briefly to melt: If your cheese is slow to melt, tent the pan with a lid for 10–15 seconds.

Variations

• Animal-Style Dutchman: Spoon the spread over the patties and pile on extra grilled onions.
• Spicy: Swap 1 tsp of the mustard per patty for Dijon and add a few dashes of hot sauce to the spread.
• Lettuce Wrap: Serve with crisp iceberg or butter lettuce leaves for wrapping the stack.

Storage & Make-Ahead

The spread can be made up to 7 days in advance; keep refrigerated. Grilled onions can be cooked 3 days ahead and reheated over low heat with a splash of water. For best texture, cook patties to order. If needed, refrigerate cooked patties up to 2 days and reheat in a hot skillet 1–2 minutes per side. Freezing is not recommended for this ultra-thin style.

Nutrition (per serving)

Approximate: 560 calories; 45 g fat; 8 g carbohydrates; 28 g protein; 1,050 mg sodium. Values will vary based on brands and exact portion sizes.