Smash burgers with baconnaise sauce take 2 lbs of 85/15 ground beef divided into 4 oz meatballs, smashed thin on a ripping hot griddle with shaved onions pressed into the surface, seasoned with salt, pepper, and garlic, and cooked 2 to 3 minutes per side until the edges are crispy and the cheese is melted. The baconnaise sauce is the real move here, made from crispy chopped bacon folded into a mix of mayonnaise, ketchup, mustard, honey, and chili flakes for a creamy, smoky, sweet, and slightly spicy burger sauce that coats both sides of a toasted brioche bun. The sauce gets better as it sits, so make it first while the griddle heats up. Stack 1 to 2 patties per burger and serve immediately while the cheese is still dripping. Serves 4 to 6.

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Why the Smash Technique Produces a Better Burger

Maximum Surface Area for the Maillard Reaction

A thick, round patty only has two flat contact points with the griddle. A smashed patty has an entire thin surface pressed directly against the hot metal, which means significantly more of the beef undergoes the Maillard reaction at the same time. That browning reaction is where the deep, savory, beefy flavor comes from, and a smash burger maximizes it by turning the entire bottom surface into a crispy, caramelized crust while the interior stays juicy from the rendered fat.

Keep the Meatballs Loose

When you divide the ground beef into 4 oz meatballs, handle the meat as little as possible. Overworking ground beef compresses the proteins and squeezes out moisture, which produces a dense, dry patty instead of a tender, juicy one. Gently roll the portions into loose balls and place them directly on the hot griddle. The smashing does the shaping for you, so there is no need to form or press the meat beforehand.

Building the Baconnaise Sauce

Cook the Bacon First

Start by cooking 12 oz of bacon (about 10 to 12 slices) until crispy. Remove the bacon from the pan, let it cool on a paper towel-lined plate, then chop it into small bacon bits. The bacon needs to be fully crispy so the bits hold their crunch when folded into the sauce. Soft or chewy bacon will turn soggy in the mayo base and lose the textural contrast that makes the sauce work.

Five Ingredients Plus Bacon

In a bowl, combine 1/2 cup mayonnaise, 1/4 cup ketchup, 3 tablespoons mustard, 3 tablespoons honey, and 1 teaspoon chili flakes. Mix until smooth and uniform, then fold in the chopped bacon bits. The mayo provides the creamy base. Ketchup adds tangy sweetness. Mustard adds sharpness and a slight acidity. Honey adds sticky sweetness that bridges the savory bacon and the tangy condiments. Chili flakes add a low-level heat that builds with each bite. Set the sauce aside while you cook the burgers, and it will taste even better by the time you are ready to assemble because the flavors meld together as they sit.

Why 85/15 Ground Beef Works for Smash Burgers

Fat Content and the Crispy Edge Equation

85/15 ground beef has enough fat to keep the patty juicy and render into the griddle surface during the cook, but not so much that the patty shrinks excessively or pools grease. Some smash burger recipes call for 80/20, which also works well and produces a slightly fattier, juicier patty. Leaner blends like 90/10 do not have enough fat to create the crispy edges and rendered surface that define a great smash burger, so avoid going below 85/15.

Portion Size and Double-Stacking

Each meatball weighs 4 oz, which produces a thin, wide patty when smashed. Two patties stacked on a single brioche bun creates the ideal ratio of crispy beef, melted cheese, and baconnaise sauce in every bite. A single patty works if you prefer a lighter burger, but the double stack gives you two layers of crispy edges and two layers of melted cheese, which is the standard for smash burger builds.

Smashing with Onions on Top

Shaved Onions Get Pressed Into the Patty

Place each meatball on the hot griddle, then add a small handful of thinly shaved onion on top before smashing. When you press the patty flat, the onions get embedded into the surface of the beef and cook directly into the meat. As the patty sears, the onions caramelize on the griddle side and fuse with the crispy edges, adding sweetness and texture that you cannot replicate by placing onions on top of an already-cooked patty.

Smash Once, Immediately, and Hard

Press the meatball flat within the first 10 seconds of placing it on the griddle. Use a sturdy burger press or the flat side of a heavy spatula and push down firmly. Only smash once because pressing again after the crust has started forming will break the seal and release the juices you are trying to keep inside. After the initial smash, do not touch the patty for 2 to 3 minutes while the bottom forms a deep, crispy crust.

Cooking, Flipping, and Melting the Cheese

Season, Flip, Cheese

After smashing, season the top side (which is now facing up) with salt, pepper, and garlic powder. Cook for 2 to 3 minutes without touching until the edges are deeply browned and crispy. Then flip each patty with a thin metal spatula, scraping under the crust to keep it intact. Season the newly exposed side, add a slice of thin cheddar or American cheese, and cook for another 1 to 2 minutes until the cheese is fully melted and the second side has formed a crust.

Toasting the Buns on the Same Surface

While the cheese melts, lay the brioche buns cut-side down on the griddle to toast. The buns pick up rendered beef fat and residual seasoning from the griddle surface, which adds flavor and creates a sturdy, toasted interior that holds up to the baconnaise sauce without getting soggy. Toast for about 1 minute until golden brown on the cut surface.

Step-by-Step: How to Make Smash Burgers with Baconnaise Sauce

Step 1: Make the Baconnaise Sauce

Cook 12 oz of bacon (about 10 to 12 slices) on the griddle or in a pan until crispy. Remove and let it cool on a paper towel-lined plate, then chop into small bacon bits. In a bowl, combine 1/2 cup mayonnaise, 1/4 cup ketchup, 3 tablespoons mustard, 3 tablespoons honey, and 1 teaspoon chili flakes. Mix until smooth, then fold in the chopped bacon bits. Set aside while you prep and cook the burgers.

Step 2: Prep the Burgers

Divide 2 lbs of 85/15 ground beef into 4 oz meatballs, handling the meat as little as possible to keep the texture loose and tender. Thinly shave 1 small onion (use a mandoline if you have one for paper-thin slices). Preheat your griddle or cast iron pan over medium-high heat until it is ripping hot.

Step 3: Smash and Cook

Place each meatball on the hot griddle surface, top with a small handful of shaved onions, and smash flat immediately using a burger press or heavy spatula. Season the top side with salt, pepper, and garlic powder. Cook for 2 to 3 minutes without touching until the edges are deeply browned and crispy. Flip with a thin metal spatula (scrape under the crust to keep it intact), season the other side, and add a slice of thin cheddar or American cheese. Cook another 1 to 2 minutes until the cheese is fully melted.

Step 4: Toast and Assemble

Lightly toast your brioche buns cut-side down on the griddle for about 1 minute until golden. Spread a generous layer of baconnaise sauce on both the top and bottom bun. Stack 1 to 2 cheesy smash patties per burger, then add extra onions or pickles if you want some crunch and acidity to cut through the richness. Serve immediately while the cheese is still melted and the baconnaise is dripping.