12 ounces russet potatoes, peeled and cut into sticks 3 inches long by 3/8 inch wide (about 2 cups)
12 ounces lean filet mignon
2 teaspoons soy sauce
2 teaspoons red wine vinegar
3 cups plus 2 tablespoons peanut or vegetable oil
1 tablespoon minced garlic
3/4 teaspoon salt
1/4 teaspoon freshly ground pepper
1 small red onion, cut into thin wedges (about 1 cup)
1 medium ripe tomato, cut into thin wedges
1/4 teaspoon sugar
1 to 3 teaspoons aji amarillo chili, seeded and cut into scant ¼-inch-thick slices
2 tablespoons chopped cilantro
Pat the potatoes dry with paper towels. Line two large plates with several sheets of paper towels. Cut the beef with the grain in half. Cut each half with the grain in half so that you have a total of 4 quarters. Cut each quarter section across the grain into ¼-inch-thick bite-sized slices. In a small bowl combine the soy sauce and vinegar.
In a 2-quart saucepan heat the 3 cups oil over medium-high heat until the oil registers 300°F on a deep-frying thermometer, making sure the tip of the thermometer does not touch the pan. Carefully add the potatoes and fry 3 minutes or until they are tender. Remove the pan from the heat. Carefully remove the potatoes with a metal skimmer and drain on one of the paper towel–lined plates. Then discard the oil-soaked paper towels (because the potatoes sometimes will stick to the towels).
Reheat the same oil in the saucepan over medium-high heat until the temperature reaches 360°F. Carefully add the same potatoes to the oil and fry until light golden, about 2 to 3 minutes. Carefully remove the potatoes with a metal skimmer and drain on the second prepared plate. Then discard the oil-soaked paper towels. Let the hot oil cool before discarding.
Heat a 14-inch flat-bottomed wok or 12-inch skillet over high heat until a bead of water vaporizes within 1 to 2 seconds of contact. Swirl in the remaining 2 tablespoons oil, carefully add the beef, and spread it evenly in one layer in the wok. Cook undisturbed 1 minute, letting the beef begin to sear.
Sprinkle on the garlic, salt, and pepper. Then, using a metal spatula, stir-fry 30 seconds, until the beef is lightly browned but not cooked through.
Add the red onions and tomatoes and stir-fry 30 seconds or until the tomatoes begins to soften. Swirl the soy sauce mixture into thewok, sprinkle on the sugar and chilies, and stir-fry 30 seconds or until well combined.
Add the cilantro and fried potatoes and stir-fry several seconds until the ingredients are combined and the beef is just cooked.
Serves 2 to 3 as a main dish or 4 as part of a multicourse meal.