Oklahoma smash burgers typically only have meat, onions, salt and cheese.

The cheapest beef from Costco is this Sirloin tip.  Chuck also works but the fridge shelf life is a little shorter.

Normally I use only fresh beef.  I buy the cheapest from Costco.

I save the fat and meat trimmings from my dry aging which I vacuum pack and freeze in small portions.  

You want a mixture of about 80-85% beef and 15-20% fat

I use the Kitchen Aid Mixer with the meat grinder attachment.  Use the larger of the two cutting dies.

Add meat and fat together.

Don't add salt at this stage.

Make sure the meat and fat is equally dispersed in the ground beef.

I use 140 gr of ground beef and found this to be the perfect amount for one burger.  Use your hands to squeeze each ball fairly tightly.

Thickly slice one to one and a half onions for 5 burgers.

Use American cheese, one slice per burger.

Smash burgers are best done on a Blackstone Grill.  You can also use a BBQ safe smooth grilling pan.

Fry the onions with some cooking oil on medium heat.  Don't brown them too much at this stage, they will continue to cook with the meat paddy.

Separate the onions into equal piles.

For the non-onion people leave an empty space for the meat paddy.

Place one burger meat ball onto each pile of onions.

Smash the beef fairly thin.

After these burgers I bought a round paddy press which works really well.

Not shown but use parchment paper between the meat and press otherwise the meat will stick to the press.

After smashing add a generous amount of salt.

Continue frying for a few minutes until that one side is done.

Turn the heat up so that the gets nice and brown.

Flip the burgers when you think the onion side is done, should only take a few minutes.

Adding a slice of cheese to the onion side will help hold everything together.

Cook for a few more minutes.

Use a soft bun like a brioche.

Keep it simple, I add only ketchup and Japanese Kewpie Mayo.