Prep ingredients: Bring a large pot of salted water to a boil. Halve leeks lengthwise, cut into 1⁄2- inch slices and rinse clean. Roughly chop cilantro, and in a measuring cup, whisk broth concentrate, 3 tablespoons tamari, and 1 cup water to dissolve.

Season beef: In a medium bowl, combine beef, cumin, 1 teaspoon crushed red pepper, remaining tamari, and 2 teaspoon of the sesame oil.

Make chili oil: In a large skillet, combine 2 tablespoons oil with remaining crushed red pepper and sesame oil and cook over low heat just until warm, but not sizzling. Carefully pour into a small bowl, and clean out skillet.

Cook beef: Heat 1 tablespoon oil in the same skillet over medium heat. Add beef mixture, stirring to break up the large pieces, and cook until fat is rendered and beef is browned, 6–7 minutes. Pour mixture into a colander to drain to get rid of fat.

Cook leeks: Add 1 tablespoon oil to skillet over high. Add leeks, cook, stirring occasionally, until softened, but still green, 4-5 minutes. Return beef to skillet and stir in 1 tablespoon flour. Add broth mixture and bring to a boil, scraping up any browned bits stuck to the skillet. Simmer over medium-low until slightly thickened, 2–3 minutes.

Cook noodles & serve: Add noodles to boiling water and cook, stirring once or twice, until tender, 6–7 minutes. Drain and rinse under hot running water; Stir in cilantro into beef mixture, and spoon over noodles. Top with remaining cilantro and serve with chili oil on the side, adding as much or as little as you like. Enjoy!