Lamb Burger with Lemon Caper Aïoli and Fennel Slaw

For this lamb burgers recipe, you'll want to splurge on good sturdy bakery buns that can absorb the extra liquid from the slaw and burger without disintegrating.

Lemon Caper Aïoli:
¼ cup salt-packed capers, rinsed
1 cup mayonnaise
2 Tbsp. extra-virgin olive oil
1 tsp. lemon zest, finely grated
3-4 Tbsp. lemon juice, freshly squeezed
1 tsp. Dijon mustard
2 cloves garlic, finely grated
sea salt

Lamb Burger:
1½ lbs ground lamb, preferably grass-fed
sea salt
4 Tbsp. extra-virgin olive oil, divided

Fennel Slaw:
3 ribs celery, thinly sliced on the diagonal
½ bulb fennel, thinly sliced
¼ cup fennel fronds, chopped (optional)
¼ large sweet onion, thinly sliced
3 Tbsp. lemon juice, freshly squeezed
2 tsp. dried mint, crushed
sea salt
black pepper, freshly cracked
4 potato or ciabatta rolls, toasted
Boquerones (marinated white anchovies)

For the Lemon Caper Aïoli:
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.  Make-Ahead: Aioli can be made 1 day ahead. Cover and chill.

For the Lamb Burger: 
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.

For the Fennel Slaw: 
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.

Assembly:  
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.

Makes 4 servings.