LAMB BURGERS WITH LEMON-CAPER AIOLI AND FENNEL SLAW

Steps:

• Lemon-Caper Aioli:
• Place capers in a small bowl and pour in warm water to cover. Let soak 20 minutes. Drain, rinse, and pat dry. Coarsely chop.
• Whisk capers, mayonnaise, oil, lemon zest, lemon juice, mustard, and garlic in a medium bowl; taste and season with salt and more lemon juice, if desired.
• Assembly:
• Shape lamb into 4 patties about 1" thick, season with salt, and let sit at room temperature 30 minutes.
• Heat 2 Tbsp. oil in a large skillet, ideally cast iron, over medium. Cook lamb patties, working in batches if needed, until browned (they won't take on as much color as a beef burger), 5-7 minutes. Turn and cook until browned on second side, about 5 minutes for medium-rare. Transfer patties to a plate and let rest 10 minutes.
• Meanwhile, toss celery, fennel, fennel fronds (if using), onion, lemon juice, dried mint, and remaining 2 Tbsp. oil in a medium bowl. Season slaw with salt and pepper.
• Generously spread aioli on cut sides of buns and build each burger with a lamb patty, 3 or 4 boquerones, and a mound of slaw. This is a messy burger, so the bib is not optional.
• Do Ahead
• Aioli can be made 1 day ahead. Cover and chill.