Smashed Hamburgers with Caramelized Onions

1. Prepare Caramelized Onions

Heat canola oil in a sauté pan over medium heat. Add sliced red onions and cook them until tender and starting to brown, about 8 to 10 minutes.

2. Caramelize Onions with Sugar and Vinegar

Sprinkle sugar over the onions, reduce heat to low, and cook for 10 to 15 minutes until deep brown. Add red wine vinegar, stir for 30 seconds to deglaze the pan.

3. Season and Shape Beef Patties

Combine dry mustard powder, kosher salt, and black pepper. Mix into ground beef and shape into four equal patties.

4. Freeze Patties for Texture

Place patties in the freezer for 15 minutes to ensure a crisp exterior and a rare interior once cooked.

5. Cook Beef Patties

Preheat a cast-iron skillet with oil over medium-high heat. Place chilled patties in skillet, press down firmly, and sear for 2½ to 3 minutes until browned and crusty.

6. Top with Onions and Cheese

Flip patties, top each with caramelized onions and grated Gruyère cheese. Cover skillet to melt the cheese, about 1½ to 2 minutes.

7. Assemble and Serve

Place each patty on a potato roll and serve with ketchup if desired.