Lamb Burgers with Lemon-Caper Aioli and Fennel Slaw

Preparation

1. Lemon-Caper Aioli:

   Step 1

   Place capers in a small bowl and pour in warm water to cover. Let soak 20 minutes. Drain, rinse, and pat dry. Coarsely chop.

   Step 2

   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.

2. Assembly:

   Step 3

   Shape lamb into 4 patties about 1" thick, season with salt, and let sit at room temperature 30 minutes.

   Step 4

   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.

   Step 5

   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.

   Step 6

   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.

3. Do Ahead

   Step 7

   Aioli can be made 1 day ahead. Cover and chill.