Smash Burgers with Caramelised Onions

Thin, crispy-edged, deeply flavourful — smash burgers are everything a great burger should be. The secret is high heat, loose beef, and a hard smash that maximises the Maillard reaction for an irresistible crust. Topped with slow-cooked caramelised onions and a tangy burger sauce, this is backyard cooking at its best. Recipe Details Prep Time: 15 minutes Cook Time: 45 minutes (including caramelised onions) Servings: 4 Difficulty: Easy Dietary Info: Dairy-free option available Vegan: No Ingredients Caramelised Onions 3 large yellow onions, thinly sliced 2 tbsp unsalted butter 1 tbsp olive oil 1 tsp brown sugar 1 tsp balsamic vinegar Pinch of fine sea salt Smash Burgers 680g (1.5 lb) 80/20 ground beef, loosely packed Fine sea salt and black pepper 4 slices aged cheddar (or American cheese for maximum melt) 1 tbsp neutral oil (for the cooking surface) Burger Sauce 3 tbsp mayonnaise 1 tbsp ketchup 1 tsp yellow mustard 1 tsp pickle brine ½ tsp garlic powder ½ tsp smoked paprika To Serve 4 brioche or potato buns, toasted Dill pickle slices Shredded iceberg lettuce Instructions Caramelised Onions Heat butter and olive oil in a heavy skillet over medium-low heat. Add sliced onions and a pinch of salt. Cook, stirring occasionally, for 35–40 minutes until deeply golden and jammy. Add brown sugar and balsamic vinegar in the last 5 minutes. Set aside. Burger Sauce Combine all sauce ingredients in a small bowl. Mix well and refrigerate until needed. Smash Burgers Divide the ground beef into 8 loose balls of approximately 85g each (do not compact them — loose packing is essential for a good smash). Heat a cast iron griddle or flat-top grill attachment over high heat until smoking. Brush lightly with neutral oil. Place 2 beef balls on the hot surface. Immediately smash each one flat with a heavy spatula or burger press, pressing firmly for 10 seconds. The patty should be thin — around 1cm. Season immediately with salt and pepper. Cook for 2–2.5 minutes without moving, until the edges are deeply browned and crispy. Flip once. Immediately place a slice of cheese on each patty. Cook for a further 60–90 seconds until the cheese is melted and the underside is browned. For a double smash burger, stack two patties. Repeat with remaining beef balls. Toast the buns cut-side down on the griddle for 30–60 seconds. Assemble: sauce on both bun halves, lettuce, patty (or double stack), caramelised onions, pickles, top bun. Serve immediately. Cook's Note 80/20 beef (20% fat) is non-negotiable here — leaner beef will not produce the same crust or flavour. Do not use a non-stick pan; you need cast iron or stainless steel to achieve the high heat required. The smash must happen within the first few seconds of the beef hitting the pan — once it starts to cook, the proteins set and you lose the ability to smash it thin. Work in batches of 2 to keep the surface temperature high.

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