Chock-full of flavor and slightly gamy, lamb needs a punch cheese—feta always gets the job done. The aioli can be made up to 2 days ahead if kept refrigerated.
- ROSEMARY AIOLI:
- ⅓ cup mayonnaise
- 1½ teaspoons lemon juice
- 1 teaspoon Dijon mustard
- 2 cloves garlic pressed
- 1 teaspoon chopped fresh rosemary
- 1 pound ground lamb
- Kosher salt to taste
- Ground black pepper to taste
- 4 ounces block feta crumbled
- 4 sesame seed burger buns
- Pickled red onions to garnish (see below)
- Baby greens to garnish
- ROSEMARY AIOLI:Whisk all ingredients together in a small bowl. Set aside.
- BURGERS: Divide lamb into 4 mounds and flatten into ⅓-inch-thick patties (about 5 inches in diameter).
- Heat a cast-iron skillet over medium-high. Season both sides of patties with salt and pepper, then cook for 3 minutes, pressing to flatten. Reduce heat to medium, flip, and top with crumbled feta. Cover and cook for 2 minutes more. Meanwhile, toast buns.
- Spread 1 to 2 tablespoons rosemary aioli on each bun bottom, top with patties, and garnish with pickled red onions and baby greens. Close burgers with top halves. Serve immediately.
PICKLED RED ONIONS: Fill a tea kettle with 2 to 3 cups water and bring to a boil. Meanwhile, heat ¾ cup apple cider vinegar with 1 tablespoon granulated sugar in a small pot until dissolved. Transfer to a glass jar. Slice 1 red onion and place slices in a fine-mesh sieve. Pour boiling water over onions and drain. Add blanched onions to glass jar—make sure they are submerged in brine—and seal. Refrigerate for at least 30 minutes and up to 3 weeks.