For future reference, try zaru udon:
First, make the sauce and leave in the fridge, covered.
Sauce: soy sauce (Japanese style, not Chinese), dashi, mirin, sake, sugar. Bring to a boil to remove the alcohol flavor, then chill. It should taste principally of soy sauce. You need about 3/4 cup per serving. Try 1/3 cup each soy and dashi, a couple Tb mirin and sake, and maybe 1 Tb sugar. Once cold, dilute with water if too strong, but it should be intense.