With only the simplest of garnishes, classic Japanese kake udon is a great way to appreciate the chewy texture and clean, wheaty flavor of homemade udon noodles. The broth is nothing more than a combination of smoky dashi (Japanese stock) and soy sauce with a little mirin and sugar for sweetness. Homemade dashi is of course best, but instant dashi prepared according to the package instructions is a solid stand-in. Look for boxes, bags or jars of instant dashi in the international aisle of the supermarket or in Asian grocery stores. To make this soup with dried udon, use about 10 ounces and boil the noodles until tender (check the timing on the package instructions, but test them a minute or so earlier), then rinse and portion them as directed below. If using purchased udon, you won’t need to shake them to remove excess starch. Shichimi togarashi is a Japanese blend of seven spices with a fiery, citrusy kick; if you like, offer it at the table as an optional garnish for sprinkling onto individual bowlfuls.