Step 1

Spread canola oil in the inside of a large cast iron skillet with a paper towel. Heat over high heat until lightly smoking. Add balls of beef and press down with the back side of a spatula until completely flattened. Season generously with salt and pepper.

Step 2

Working quickly, spread onions evenly over cooking burgers and press down to embed onions into meat. Let cook with no further pressing until burgers are well browned, about 2 minutes.

Step 3

Carefully flip burgers with a stiff spatula, making sure to pick up all browned meat from skillet. Let cook until onions start to soften, about 1 minute. Add cheese and top with top bun. Place bottom bun upside-down over top bun to allow it to steam in the onion vapors.

Step 4

When buns are soft, transfer bottom buns to a plate. Add condiments if desired. Lift up onions, burger, and top bun together and transfer to bottom bun. Repeat with second burgers. Serve immediately.