Smash Burgers with Caramelised Onion and Aioli

The smash burger has become one of the biggest food trends in New Zealand right now, and for good reason. Unlike a standard thick patty, a smash burger is pressed flat against a screaming hot surface the moment it hits the pan, creating a thin, lacy, deeply caramelised crust that a regular patty simply cannot produce. Paired with sweet, slow-cooked caramelised onion and a simple garlic aioli, this is a burger built entirely around technique rather than a long ingredient list.

Why the Smash Technique Works

The science is straightforward. Pressing a loosely packed ball of mince flat against a very hot pan or flat-top drives intense, even contact between the meat and the surface, triggering the Maillard reaction across the entire face of the patty rather than just the edges. The result is a thin patty with a disproportionate amount of crust, which is where almost all the flavour in a smash burger comes from.

Fat content matters more here than in a standard burger. An 80/20 beef-to-fat ratio keeps a thin patty juicy even with the high heat and short cook time, which is why a dedicated smash mince blend outperforms a leaner everyday mince for this specific job.

Ingredients

For the caramelised onion:

2 tablespoons butter
2 large onions, thinly sliced
1 teaspoon brown sugar
1 tablespoon balsamic vinegar
Pinch of salt

For the aioli:

1/2 cup good-quality mayonnaise
2 garlic cloves, finely grated
1 teaspoon lemon juice
Pinch of salt

For the burgers:

600g smash beef patty mince (80/20 blend)
Sea salt, for seasoning
4 burger buns, split
4 slices cheese (optional)
Butter, for toasting the buns
Lettuce, sliced pickles, and tomato, to serve

Method

Caramelise the onion first. Melt the butter in a pan over medium-low heat, add the onions and a pinch of salt, and cook slowly for 25 to 30 minutes, stirring occasionally, until deeply golden and soft. Stir through the brown sugar and balsamic vinegar in the last few minutes and set aside.

Make the aioli. Combine the mayonnaise, garlic, lemon juice, and salt in a small bowl. Set aside, or refrigerate if making ahead.

Portion the patties. Divide the mince into four loosely formed balls, roughly 150g each. Do not compact them, a loose ball smashes more evenly.

Heat the pan. Get a heavy flat pan, griddle, or cast iron skillet very hot, close to smoking.

Smash. Place a ball of mince on the hot surface and immediately press it flat with a burger press or the base of a heavy pan, pressing hard to around 5 to 6mm thick. Season the top with sea salt.

Sear. Cook for 2 to 3 minutes without moving the patty, until a deep crust has formed and the edges look crisp. Flip, add cheese if using, and cook for a further minute.

Toast the buns. Butter the cut sides of the buns and toast them in the same pan for 30 to 60 seconds until golden.

Build the burgers. Spread aioli on both cut sides of the bun, layer lettuce, the patty, caramelised onion, pickles, and tomato, then close and serve immediately.

A Few Notes on Getting This Right

Do not overwork the mince. Handle it as little as possible when forming the balls, overworking makes for a denser, tougher patty.
Commit to the smash. A hesitant, light press will not generate the same crust as one firm, confident press at the start.
Cook in batches if needed. Overcrowding the pan drops the surface temperature and stops the crust from forming properly.

Make-Ahead Tips

The caramelised onion and aioli can both be made up to three days ahead and kept in the fridge, which makes this a much faster weeknight meal if the toppings are already done. The patties themselves are best smashed and cooked fresh, since the crust is the whole point and it does not hold up to reheating.

The Matangi Difference

Our Smash Patty Mince is a dedicated 80/20 blend made specifically for this technique, dry-aged for three weeks like every other Matangi cut before it is ground. Order the 500g pack for this recipe, or browse our full Beef Mince and Patties range for more everyday options.

Pair it with our Ironclad Burger Press for consistent, restaurant-style results every time, or explore the wider Matangi Angus Beef range.