Asian Noodle Soup with Winter Vegetables and Tofu

Ingredients in this Recipe

1 six inch square dried kombu
1/2 large sweet potato (about 4 ounces), peeled, halved lengthwise, and cut crosswise into 1/4 inch thick slices
1/4 cup plus 1 teaspoon reduced sodium soy sauce
2 tablespoons mirin
3 ounces kohlrabi, peeled and cut into 1/4 inch thick sticks
3 ounces snow peas, trimmed and halved
3/4 cup bonito flakes (1/4 ounce)
4 ounces fresh shiitake mushrooms, stems trimmed and reserved, caps cut into 3/4 inch slices
6 cups water
6 ounces soba noodles (2 bundles)
8 ounces silken tofu, cut into 8 slices

See Full Recipe at Martha Stewart