Ingredients

For the Burgers:

• 2 tablespoons olive oil, plus more for grill
• 4 large leeks, white and light green parts only (about 1 pound), halved, rinsed well, and thinly sliced
• Kosher salt
• ¼ teaspoon cayenne pepper
• 2 pounds ground beef (preferably 80% lean) 
• ¼ cup plain dried bread crumbs 
• Freshly ground black pepper

For Assembly:

• 8 burger buns, halved 
• Mayonnaise
• Dijon mustard
• Thinly sliced red onions
• Torn butter lettuce 
• Sliced tomatoes

Directions

Make the burgers: In a large skillet, heat the olive oil over medium-high heat. Add the leeks with a heavy pinch of salt and cook, stirring often, until jammy and caramelized, 12 to 15 minutes. Remove from the heat and stir in the cayenne. Let cool completely.

In a large bowl, combine the cooled leek mixture with the ground beef and bread crumbs. Mix with your hands until just combined, then form into 8 burger patties about 1 inch thick, and make a very light indentation with your thumb in the center of each.

Start a charcoal fire or heat a gas grill to high. Dip a rolled-up paper towel in olive oil and, using tongs, brush the grates of the grill to grease. Season both sides of each patty with a heavy pinch of salt and black pepper. Place the patties on the grill and cook undisturbed until golden, 3 to 4 minutes, then flip with a metal spatula and continue to cook for another 3 to 4 minutes for medium-rare. Transfer to a platter and let rest for 5 minutes.

For assembly: Serve on the challah buns, with mayo, Dijon, thinly sliced red onions, lettuce, and tomatoes.