Cut 3 large russet potatoes into ¼ inch thick strips. Pat them completely dry with paper towels. Heat 2 inches of vegetable oil in a heavy skillet to 350°F (175°C). Fry the potatoes in batches for 5-7 minutes until golden and crispy. Drain on paper towels and season immediately with salt.
3 large russet potatoes, as needed vegetable oil, to taste salt
Cut 1.5 lbs beef sirloin against the grain into ¼ inch thick strips. Season with salt and black pepper. Let the beef sit at room temperature for 5 minutes. Preheat your wok or large cast iron skillet over high heat for 5 minutes until smoking hot.
1.5 lbs beef sirloin, to taste salt, to taste black pepper
Add 1 tablespoon vegetable oil to the hot pan. Cook half the beef strips in a single layer for 90 seconds without moving them. Flip and cook another 60 seconds until browned but still medium-rare inside (130-140°F/54-60°C). Transfer to a plate and repeat with the remaining beef.
1.5 lbs beef sirloin, as needed vegetable oil
Add another 1 tablespoon oil to the hot pan. Toss in 1 large red onion cut into thick wedges and stir-fry for 2 minutes until slightly softened but still crisp. Add 3 roma tomatoes cut into wedges, 1-2 sliced yellow chilies, and 3 minced garlic cloves. Stir-fry for 1 minute until fragrant.
1 large red onion, 3 roma tomatoes, 1-2 yellow chilies (ají amarillo), 3 cloves garlic, as needed vegetable oil
Return the beef to the pan along with the fried potatoes. Pour in 3 tablespoons soy sauce and 2 tablespoons white vinegar. Toss everything together for 30 seconds until the sauce coats the beef and vegetables. Remove from heat immediately. Garnish with fresh cilantro and serve over white rice.
1.5 lbs beef sirloin, 3 large russet potatoes, 3 tbsp soy sauce, 2 tbsp white vinegar, to taste fresh cilantro
