Steamed Manila Clams With Udon

Name: Steamed Manila Clams With Udon
Ingredients: 2 1/2 quart water; 1 x (4- to 6-inch) square kombu (dried kelp); 1 tbsp instant hon dashi (soup stock) granules; 3 tbsp light soy sauce; 1 x leek, white part only, coarsely chopped; 2 cup firmly packed katsuobushi (dried bonito flakes); Salt; 4 cup water; 3 lb Manila clams, scrubbed; 3/4 lb dried udon noodles; 2 packages (3 ½-ounce) enoki mushrooms, roots trimmed and separated into small bunches; 1 bunch fresh chives, cut into 1-inch pieces; 2 sheets toasted nori, cut into 1-by-1/4-inch strips