Ingredients

  • 1 large egg yolk*
  • 2 teaspoons Dijon mustard
  • 1/2 cup vegetable oil
  • 1 canned chipotle chile in adobo, finely chopped
  • 1 garlic clove, finely grated
  • 2 teaspoons finely grated lemon zest
  • 1 tablespoon fresh lemon juice
  • Kosher salt
  • 4 plum tomatoes, cored, halved lengthwise
  • 1 tablespoon thyme leaves
  • 1 tablespoon plus 2 teaspoons olive oil
  • 1 1/2 teaspoons kosher salt, plus more
  • Freshly ground black pepper
  • 1/2 pound thick-cut bacon, cut into pieces
  • 1 pound ground lamb, preferably from the shoulder
  • 3 tablespoons finely chopped fresh oregano
  • 3 tablespoons finely chopped fresh sage
  • 4 brioche buns, toasted
  • 1/3 pounds fresh mozzarella, thinly sliced
  • 3 cups baby arugula
  • 1 teaspoon Sherry vinegar or red wine vinegar

Method

  • Whisk egg yolk and mustard in a medium bowl to combine. Whisking constantly, gradually drizzle in oil, drop by drop at first; keep going until aioli is thickened and smooth. Whisk in chipotle, garlic, lemon zest, and lemon juice; season with salt. Cover and chill.
  • Aioli can be made 1 day ahead. Keep chilled.
  • Preheat oven to 225°. Toss tomatoes, thyme, and 1 tablespoon oil on a baking sheet; season with salt and pepper. Arrange tomatoes cut side down and roast until skin is slightly browned and beginning to separate from flesh, 75-85 minutes. Let cool, then slip off skins.
  • While tomatoes are roasting, freeze bacon until almost frozen through, about 40 minutes (this will help it chop cleanly in the food processor). Pulse bacon in a food processor, scraping down sides of bowl as needed, until very finely chopped, about 1 minute.
  • Transfer bacon to a medium bowl and gently mix in ground lamb, oregano, sage, and 1 1/2 teaspoons salt just to combine. Divide meat into 4 equal portions and gently shape into 3/4"-thick patties.
  • Heat a grill pan or a cast-iron skillet over medium-high. Cook patties until lightly charred and medium-rare, about 2 minutes per side. Generously spread buns with aioli and build burgers with patties, roasted tomatoes, and mozzarella.
  • Toss arugula in another medium bowl with vinegar and remaining 2 teaspoons oil; season with salt and pepper.
  • Serve burgers with arugula alongside.