Make the mentsuyu
-
Stir together 4 cups water, bonito flakes, soy sauce, mirin, brown sugar, and shiitake in a medium saucepan over medium-low, and slowly bring to a simmer. Simmer until flavors meld, about 5 minutes. Remove from heat, and add kombu. Let stand 10 minutes. Pour mixture through a fine wire-mesh strainer into a bowl; discard solids. Cool at room temperature 30 minutes. Cover and refrigerate at least 2 hours or up to 3 days.
Make the chashu and marinated eggs
-
Place pork, garlic, ginger, and crushed red pepper in a large Dutch oven; add water just to cover. Bring to a boil over high. Reduce heat to low, cover, and simmer until pork is just tender, about 1 hour and 30 minutes.
-
Meanwhile, bring a medium pot of water to a boil over high. Add eggs, and cook 6 minutes. Immediately transfer eggs to a bowl of ice water. Let cool 10 minutes. Carefully peel eggs, and set aside.
-
Stir together soy sauce, brown sugar, and mirin. When pork has finished braising, add soy sauce mixture to pan; stir. Simmer over low, covered, until pork is fork-tender, about 15 minutes. Remove pan from heat, and add peeled eggs. Let pork and eggs cool in liquid, uncovered, 1 hour.
Make the sesame vinaigrette
-
Place sesame seeds, rice vinegar, soy sauce, sugar, and black pepper in a blender. Process until seeds are roughly chopped, about 5 seconds. With blender running, slowly pour in sesame oil to emulsify, about 30 seconds.
-
Pat drained noodles dry. Divide cold noodles evenly among 4 bowls. Thinly slice pork; cut eggs in half. Top noodles evenly with pork and eggs. Drizzle each with about 1 tablespoon sesame vinaigrette. Pour about 1/4 cup chilled mentsuyu down side of each bowl. Garnish with scallions, sesame seeds, Chinese mustard, radish, zucchini, shiso, and basil, if desired.
Make Ahead
Chashu pork and marinated eggs can be prepared through step 4, covered, and chilled up to 3 days. Let stand at room temperature for 30 minutes before proceeding. Mentsuyu and sesame vinaigrette can be prepared up to 3 days ahead; cover and chill until ready to serve.
Notes
Shirakiku Hana Tororo Soba was our testers’ favorite brand; find it at well-stocked Asian supermarkets.
Suggested Pairing
Light-bodied, aromatic Muscadet.