Instructions

Pulse tomatillos in food processor until coarsely chopped, about 8 pulses. Transfer to fine-mesh strainer set over bowl and let drain for 5 minutes; reserve 3/4 cup liquid. Combine half of jalapeños, 1/4 cup cilantro, half of garlic, drained tomatillos, and 1/4 cup reserved tomatillo liquid in bowl. Season with salt and pepper to taste.
Pat steak dry and season with salt and pepper. Heat 2 tablespoons oil in 12-inch nonstick skillet over medium-high heat until just smoking. Cook steak until browned all over and meat registers 125 degrees (for medium-rare), 6 to 8 minutes. Transfer to plate and tent loosely with aluminum foil. Add remaining 1 tablespoon oil and onion to now-empty skillet and cook over medium heat until just softened, about 2 minutes. Add cumin, remaining jalapeño, and remaining garlic and cook until fragrant, about 30 seconds. Add beans and remaining 1/2 cup reserved tomatillo liquid. Using potato masher, coarsely mash beans. Cook, stirring occasionally, until thickened, about 3 minutes. Stir in remaining 1/4 cup cilantro. Season with salt and pepper to taste. Serve steak with beans and salsa.