Smashburger with Stone Ground Mustard Aioli

Feeds four people
Makes four double smashburgers (eight patties total)

INGREDIENTS
Smashburger
1 lb. United Harvest ground beef, cold and divided into approximately 0.14 lb. balls or 2-inch balls (for a total of 8 balls)
Kosher salt and ground pepper, to season the burger patties
Canola oil spray
1 yellow onion, very thinly sliced using a mandoline (if possible)
8 slices American Cheese
Iceberg lettuce, very thinly sliced
2 large round tomatoes, cut into 1⁄4-inch thick slices
Dill pickle chips
Stone ground mustard aioli (recipe below)
8 potato rolls or brioche buns

Stone Ground Mustard Aioli
1 cup good quality mayonnaise
6 tbsp. stone ground mustard
2 tsp. garlic powder
1⁄2 tsp. salt, or to taste
1⁄2 tsp. black pepper, or to taste

DIRECTIONS
For the mustard aioli:
● In a medium bowl, whisk all ingredients together. Set aside until ready to use.

For the smashburgers:
● Divide the ground beef into 0.14 lb. balls or 2-inch balls and place in the refrigerator, covered with plastic wrap, until ready to cook.
● Using a mandoline, cut the onion into very thin slices. Place in a bowl and set aside.
● Heat a non-stick flat grill pan (without ridges) over high heat (the highest you can go) and let warm up for approximately 5 minutes. Lightly coat the grill pan with canola oil spray.
● While the grill pan is heating, season the cold ground beef balls with salt and pepper.
● Once the pan is hot, place two balls on the grill pan and immediately top each ball with a generous amount of thinly sliced onions.
● Using two-handed pressure and moving quickly, smash one patty at a time applying pressure with both hands using a wide metal hamburger spatula (ideally 4 inches wide) and your other hand in an oven mit. Smash burgers to approximately 1⁄4-inch thick. Repeat with the other ball of meat.
● Cook the burgers approximately two minutes then flip burger patties and onions together. Immediately place one slice of American cheese on each patty then cover with a dome shaped lid to melt the cheese.
● After about 20-30 seconds, the cheese should be melted. Remove the lids and transfer the burger patties to a cutting board using the hamburger spatula.
● Repeat the process with the remaining 6 balls of ground beef. Let the burger patties sit a few minutes to let the juice seal.
● Once all burger patties are cooked, toast the buns to desired doneness.
● To assemble the smashburgers, spoon a generous amount of the stone ground mustard aioli on the bottom bun. Next, top with a handful of shredded iceberg lettuce, one tomato slice, two cheeseburger patties with grilled onions and 2-3 dill pickle chips. Spread additional stone ground mustard aioli on the top bun, then place on the burger and serve.