Step 1Bring the kombu and water to a boil and cook 15 minutes. Remove from the heat and add the bonito flakes. Let sit until the bonito flakes sink to the bottom of the liquid, about 20 minutes. Strain and discard the flakes.
Step 2Add the soy sauce and mirin to the broth and return to a boil. Remove from the heat and cool until ready to use. The broth can be prepared several hours in advance. Makes 8 cups.
Step 1In a large braising pan or Dutch oven, heat the oil over medium heat. Brown the pork belly on the skin side. Turn the belly over and brown the other side; this will take about 20 minutes in all. Remove the meat from the pan and set aside.
Step 2Add the green onions, ginger, carrot and celery and cook until lightly brown, about 3 minutes. Add the wines; reduce by half.
Step 3Add the soy sauce, mirin, water and star anise. Bring to a boil and simmer for about 5 minutes.
Step 4Heat the oven to 400 degrees. Return the meat to the braising liquid and cover the pan with a sheet of parchment paper or foil. Cover tightly with a lid, place in the oven and cook until the meat is fork tender, about 2 1/2 hours.
Step 5Remove the pan from the oven and let stand until ready to serve.The pork belly can be prepared in advance and kept for several days in the refrigerator, covered in the braising liquid.
Step 1Cook the bok choy in a large pot of rapidly boiling water until barely tender and still a little crisp, 1 to 2 minutes. Remove the bok choy (reserve the water) and place it in a bowl of ice water. Can be done up to 3 hours ahead.
Step 2Just before serving, heat the udon dashi and warm the baby bok choy and bamboo shoots in it.
Step 3Cook the udon according to package directions in the same pot of boiling water used for the bok choy.
Step 4Divide the udon among 8 large, deep serving bowls. Cut the pork belly into 8 servings and place on top of the udon. Pour about one-fourth cup of braising liquid over each serving. Arrange the bok choy and bamboo shoots around the outside of the pork and add 1 cup of the udon dashi. Garnish with green onions and serve.