Grilled Cast Iron Smash Burgers

June 21, 2021

Forget those grill marks or meat loaf patties! Grilled cast iron smash burgers is where it’s at with all that caramelized onion and juicy burger goodness. All you need is a few ingredients and a few easy steps to take your BBQ to the next level.

Grilled Cast Iron Skillet Smash Burgers - sarcastic cooking

I have a mostly year round frozen pizza and beer Friday series over on Instagram.

I hope you guys know about that already.

Pizza and beer Friday becomes BBQ and brews Friday in the summer.

The first installment for this summer was these epic grilled cast iron smash burgers.

They are my go to burger for all seasons.

I prefer to make them outdoors on the grill to prevent smoking out the house and grease splatter clean up.

That isn’t to say I haven’t had a smash burger craving in the winter and just cooked them indoors on the stove.

smash burgers - sarcastic cooking

There are a few key ingredients to making these burgers:

a cast iron skillet

a tablespoon or two of unsalted butter

85% – 80% lean ground beef

salt and pepper

thinly sliced yellow onion

American cheese

brioche buns

The reason these burgers have become a staple is mainly because they are so easy to make.

Cast Iron Skillet Smash Burgers | Sarcastic Cooking

They really are hard to mess up, unlike those fat, meatloaf-like patties.

Mike always gets stressed when somebody (cough, Dad) asks for a rare cook on their meat.

It is hard to manage cooking burgers for an entire BBQ on the same grill at different levels of doneness.

You can easily turn these into double stack burgers if somebody is super hungry.

The butter and the fact that the meat is not super lean help to keep these thin patties juicy.

Do not question the American cheese.

The almighty Kraft Single kneels for no man.

I know that smashing a burger may go against everything you ever learned about grilling in your life, but trust me.

The meat is protected in the cast iron and all the juices and flavors from the slivered onions infuse throughout the whole burger cooking process.

You can easily skip the onions as well, if let’s say you have anti-onion folks aka kids to feed.

Copycat In n Out Burger | Sarcastic Cooking

As long as you cook a few burgers with the onions before you cook the onion-less ones, that slight onion flavor will still be there in the background.

Toppings wise I go big.

Gimme all the pickles, tomato, lettuce, and burger sauce or Trader Joe’s Magnifisauce

Trust the process and the next thing you’ll be saying is, “Shake Shack/ In-n-Out who?”

Cast Iron Skillet Smash Burgers | Sarcastic Cooking

Grilled Cast Iron Smash Burgers

Yield: 10 Single Burgers
Prep Time: 10 minutes
Cook Time: 20 minutes
Total Time: 30 minutes

Thin and juicy smash cheese burgers cooked in a cast iron skillet on the grill with caramelized onions and a little butter.


  • 2lbs 80% or 85% lean ground beef
  • a pinch of kosher or maldon salt and a few grinds of black pepper per burger patty
  • 1/2 yellow onion, thinly sliced or slivered
  • 1-2 tbsp unsalted butter
  • 10 slices of American cheese
  • 10 brioche burger buns or brioche sesame seed burger buns


  1. Preheat your grill with a large cast iron skillet in the center of the grates. Put all gas burners on high until the temperature is above 475 degrees F.
  2. While the grill preheats, divide the ground beef into 10 equal portions or squares with a knife. Roll each square into a meatball. Place the meatball between two large pieces of either plastic wrap or parchment paper. You may have to do two different batches of 5 between two pieces of paper/plastic. Once the meatballs have all been portioned out and placed between the paper/plastic, use a large baking sheet to press down evenly until the patties are less than 1/4 of an inch thick.
  3. Season the patties with a good pinch of salt and pepper.
  4. Thinly slice the half of a yellow onion.
  5. Carry the burgers out to the grill. Open the lid, add the butter to the hot cast iron. Use a spatula to make sure it coats as much fo the cast iron as possible.
  6. Add 3 or 4 patties at a time to the skillet. Smash each down with the spatula. Top each patty with a few slivered onions. Cook for about 4 minutes on the first side. You can leave the lid open the whole time the burgers cook.
  7. Flip the burgers and have the onions between the pan and the beef. Smash the patties down with the spatula. Cook for another 4 minutes. During the last minute, top each patty with a slice of American.
  8. While the second side cooks, I recommend toasting your buns on the open grill grates for a minute or two.
  9. Carefully remove the burgers and the caramelized onions from the grill, transfer to the bottom bun, and do not top with the top bun piece. People can put toppings on easier if the cheese doesn't get stuck to the top bun.
  10. Cook the burgers in batches of 3-4 until all burgers are done. Be sure to close the lid for a few minutes between batches to let the cast iron heat up again.
  11. Burgers can be served as singles or doubles. If you make doubles, clearly you only need 5 buns.


WARNING: Beware that when you do smash down the burgers, they will sometimes splatter. Stand as clear as you can and wear an apron to prevent burns and stains from the grease.

Smash Burgers Cooked on the Grill in a Cast Iron Skillet | Sarcastic Cooking

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  • randall morean
    June 22, 2021 at 8:02 am

    I think you misspoke when in step 7 you say “Flip the burgers and have the onions between the patty and the beef.” Between the pan and the beef is more likely what you meant. We love smash burgers with some fish sauce in the mix. Thanks for a great variation

    • Stefanie
      June 22, 2021 at 12:41 pm

      Yes! 🤦🏼‍♀️ Good catch. I’ll fix it. I was working on this post kid bedtime and a bit sleepy hahaha

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