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Beef and Onion Smash Burgers

Paper-thin onions are smashed into loose beef on searing cast iron, where they turn crisp and bronze before the buns soften briefly in the heat.

A soft bun holds a thin beef patty edged with crisp browned onions, mustard, and dill pickle chips.

The defining move in an El Reno-style onion burger is to cook the onions with the beef, pressing them into the patty rather than browning them separately. A hot cast-iron surface and a patient first side create the characteristic lacy crust.

Slice for full contact

Shave the onions very thin so they can flatten into the beef and cook through before the patty dries. Dividing them evenly before the skillet gets hot keeps the short cooking sequence easy to manage.

Keep the beef loose

Form the ground beef only enough to make portions that hold together, then smash them firmly once they hit the skillet. That single press creates wide contact for browning while leaving the inside tender.

Paper-thin yellow onions are pressed into a loosely formed beef patty on cast iron. — Thin onion shavings are pressed into loosely formed beef on hot cast iron.

Wait for the lacy edge

The first side needs undisturbed contact to develop a deep brown crust. When the edges are crisp and lacy and the onions are softened, a thin spatula can scrape underneath without leaving the best browned bits behind.

Finish quickly and serve hot

After the flip, the thin patties need only a short finish; check the center with a thermometer and stop cooking as soon as it reaches the safe temperature. A brief covered steam softens the buns, while mustard and pickles add sharpness against the rich beef and sweet onion.

A close view shows crisp browned onion lace fused to beef beneath a soft bun with mustard and pickles. — The finished burger shows crisp onion edges against a soft bun with mustard and pickles.

If the crust resists

If the patty does not lift cleanly, give it a little longer rather than forcing the spatula under too soon. Scrape all the way across in one deliberate motion, and avoid pressing the meat again after its initial smash.

Beef and Onion Smash Burgers

4 burgers

35 minutes total

Ingredients

• 1 1/2 lb 80/20 ground beef
• 3 medium yellow onions (about 1 lb total), peeled
• 1 tsp kosher salt
• 1/2 tsp freshly ground black pepper
• 4 soft hamburger buns
• 2 tbsp yellow mustard
• 16 dill pickle chips

Method

Shave the onions
Slice the peeled yellow onions paper-thin with a sharp knife or guarded mandoline, then divide the shavings into four equal loose piles so each burger gets a generous layer.
Look for: The onion shavings are thin and flexible, not thick half-moons.
Portion the beef
Gently divide the ground beef into four equal portions and roll each just enough to hold as a loose ball; avoid packing or kneading it, which can make the thin patties dense.
Look for: Each portion holds together lightly and still looks loosely textured.
Set out the buns and toppings
Split the hamburger buns and set them beside the griddle with the yellow mustard and dill pickle chips, keeping the toppings ready for quick assembly.
Look for: The buns are split and the mustard and pickle chips are within reach.
Heat the cast iron
Heat a large cast-iron griddle or skillet over high heat for 6 to 7 minutes, until the surface is very hot with a faint wisp of smoke; ventilate the kitchen and have a thin, sturdy spatula ready.
Look for: The cast iron is evenly hot and just begins to wisp, not billow, smoke.
Smash with onions
Cook two burgers at a time: place two beef balls on the hot cast iron with room between them, top each with one onion pile, then firmly smash for about 10 seconds until very thin and the onions are pressed into the beef. Sprinkle the salt and pepper evenly over the exposed surfaces.
Look for: Each patty is thin, its onions are embedded, and the beef has broad contact with the griddle.
Build the lacy crust
Leave the patties untouched for 2 to 3 minutes; do not press again. Wait until the edges are deeply browned and lacy, the onions look softened with bronzed tips, and juices bead on the top before turning.
Look for: A dark, crisp edge releases around most of each patty and onion strands are softened.
Scrape, flip, and finish
Drive the spatula fully under each browned crust and flip in one confident motion, then cook 1 to 2 minutes. Check a patty from the side with an instant-read thermometer; the center must reach 160 F, so if it is short, lower heat to medium-high and cook in brief 20-second intervals.
Look for: The crust stays attached as the burger turns and the center reaches 160 F.
Steam the buns briefly
Set each cooked patty on a lower bun on the warm griddle, place its top bun half over the patty, and cover with a lid or inverted heatproof bowl for 20 to 30 seconds. Repeat for the second batch; the trapped heat softens the buns without holding the beef over direct heat.
Look for: The bun tops feel warm and supple, not wet or collapsed.
Dress and serve
Lift the bun tops, spread yellow mustard over them, add four dill pickle chips to each burger, and close the buns. Serve immediately while the onion crust remains crisp and the beef juicy.
Look for: Each burger has mustard and pickle chips and is served as soon as assembled.