How to Make It
Preheat the broiler with the rack 6 inches from the heat. Spread the tomatillos, jalapeños, onion and garlic on a rimmed baking sheet and toss with 2 tablespoons of the olive oil; season with salt and pepper. Broil for about 15 minutes, stirring once, until the tomatillos and onion are softened and lightly charred in spots. Let the vegetables cool to room temperature, then scrape them into a blender. Add the cilantro and puree until smooth. Season the salsa with salt and pepper.
Meanwhile, light a grill or preheat a grill pan and brush with oil. Rub the steak all over with the remaining 2 tablespoons of olive oil and season with salt and pepper. Grill over moderate heat, turning once, until the meat is nicely charred, about 3 minutes per side for medium-rare. Transfer the steak to a work surface and let rest for 5 minutes. Thinly slice against the grain and serve with the tomatillo salsa.