Inspired by stir-fried Peruvian steak and potatoes—lomo saltado—here the potatoes and steak are cooked separately to keep the potato wedges crispy on the outside and to get a nice sear on the steak. To save time, we use prepared pico de gallo (fresh tomato salsa) to add fresh flavor to the tomatillo sauce instead of making salsa from scratch. Depending on your market, individual flank steaks might be large.
How to Make It
Cut potato into 8 (1/2-inch-thick) wedges. Combine potato wedges, 1 1/2 teaspoons cumin, and 1/4 teaspoon salt in a bowl; toss to coat. Heat 1 tablespoon of the oil in a large nonstick skillet over medium-high; add potatoes. Cook, turning often, until potatoes begin to brown, about 5 minutes. Reduce heat to medium; cook until potatoes are golden brown, about 15 minutes. Add onion; cook, stirring occasionally, 4 minutes. Remove from heat; keep warm.
Meanwhile, heat a medium cast-iron skillet over medium-high. Add tomatillos and jalapeño; cook until charred on all sides, about 8 minutes. Remove from heat. Combine tomatillos, jalapeño, pico de gallo, 2 teaspoons lime juice, and 1/4 teaspoon salt in the bowl of a mini food processor. Process until finely chopped, about 1 minute.
Heat remaining 1 tablespoon oil in cast-iron skillet over medium-high. Season both sides of steak with coriander, remaining 1/4 teaspoon salt, and remaining 1 1/2 teaspoons cumin. Add steak to skillet; cook to desired degree of doneness, 4 to 5 minutes per side for medium-rare. Remove to a cutting board; let stand 5 minutes.
While steak rests, toss cooked potato wedges and onions in a large bowl with cilantro, queso fresco, and remaining 1 teaspoon lime juice. Cut steak against the grain into thin slices; drizzle with the tomatillo sauce. Serve steak and sauce with potato mixture.