2 Tbsp low-sodium soy sauce
1/4 tsp crushed red pepper
3 garlic cloves, minced
8 ounces flank steak, cut into 1 1/2-inch wide strips and thinly sliced
6 cups stock (4 beef and 2 chicken is optimal)
2 cups water
2 tablespoons fish sauce
2 teaspoons brown sugar
2-4 whole cloves (about 1/4 teaspoon ground clove)
3 star anise (or 1 teaspoon fennel seed)
1 (3-inch) cinnamon stick, broken (about 1/2 tsp ground cinnamon
1 (3-inch) piece peeled fresh ginger, halved
3 garlic cloves
1 Tbsp peanut or canola oil
1 medium onion, thinly sliced
6 cups thinly sliced bok choy (about 1 pound)
1 cup (about 2 ounces) shiitake mushrooms, thinly sliced
1 cup carrot, sliced
1/2 cup green onions, thinly sliced
2 Tbsp hoisin sauce
4 ounces uncooked soba (buckwheat) noodles
1 Tbsp rice vinegar
1 1/2 tsp dark sesame oil, divided
Combine the first 4 ingredients in a large zip-top plastic bag, and seal. Marinate in refrigerator 2 1/2 hours, turning bag occasionally.
Combine the next 9 ingredients in a large stockpot over medium-high heat; bring to a boil. Reduce heat, and simmer 30 minutes covered. Strain broth through a sieve into a large bowl; discard solids. Return broth to pan; keep warm.
Heat oil in a small Dutch oven over high heat until it begins to smoke. Add beef mixture to pan; stir-fry 1 minute or until browned. Remove beef mixture from pan; set aside.
Add sliced yellow onion to the pan and cook until tender and starting to color. Add bok choy, mushrooms, carrot, and green onions to pan; stir-fry 2 minutes or until bok choy begins to wilt. Add prepared broth mixture and hoisin sauce. Stir in noodles. Reduce heat; simmer 5 minutes or until noodles are done. Stir in beef mixture and vinegar. Ladle 1 1/2 cups soup into each of 6 bowls; drizzle each serving with 1/4 tsp sesame oil.