Skirt steak is one of our favorite cuts -- it's quick-cooking and full of flavor.
In a blender, combine buttermilk, cilantro, coriander seed, curry powder, and scallions and puree. Reserve 1/2 cup marinade for serving. Pour half the remaining marinade into a shallow dish, arrange steak in a single layer, and cover with rest of marinade; let sit 30 to 45 minutes.
Heat a grill or grill pan to medium-high. Clean and lightly oil hot grill. Remove steak from marinade, shaking off excess, and season with salt and pepper. Grill steak until browned, 2 to 4 minutes per side for medium-rare. Transfer to a cutting board and let rest 5 minutes before thinly slicing against the grain. Season reserved marinade with salt and pepper and serve with sliced steak.
Double DutyWe use this marinade as a dipping sauce, too. Try it with pork, chicken, or fish.