Sid'S Onion Burger - cooking recipe

Ingredients

4 tablespoons canola oil
1 lb ground beef (gently formed into 6 balls)
2 medium yellow onions (very thinly sliced with a mandoline or a sharp knife and divided into 6 equal portions)
kosher salt, to taste
6 slices American cheese
6 hamburger buns, toasted

Preparation

Working in 2 batches, heat 2 tablespoons oil in a 12\" cast-iron skillet over medium-high heat.
Add 3 beef balls and, using the back of a spatula, press down on them until they're thin; cook for 1 minute.
Top each patty with a portion of the onions; season with salt.
Press onions into the meat and cook for 1 minute more.
Flip burgers; flatten with the spatula. Place a cheese slice on each patty and let melt while onions and meat brown.
Serve on buns.