Spring Lamb in Herbs

Name: Spring Lamb in Herbs
Ingredients: 2 Tbsp. coriander seeds; 2 Tbsp. fennel seeds; 1 bunch cilantro; 1 bunch dill; 3 small bunches tarragon; 4 scallions or spring onions, thinly sliced; 2 small preserved lemons, skin and flesh chopped; 4 garlic cloves, coarsely chopped; 1/4 cup extra-virgin olive oil, plus more for serving; 2 tsp. kosher salt, plus more; 1 (6–7-lb.) bone-in leg of lamb; 4 lb. baby Yukon Gold potatoes; 2 lemons, cut into wedges; Flaky sea salt