This is one of our favorite Japanese dishes because the dashi and the egg work beautifully together in delicate harmony. Additionally, this dish is great because you can add whatever cooked ingredients you like: crab, chicken, turnips, fish, daikon, shrimp, etc.
Note: Hardest part about making chawan mushi is finding the best vessel to steam in. Ideally a small teacup is best.
On the stove top, set up a steamer basket that will be able to hold 6 to 8 vessels. Fill with water and turn on high heat to start the steamer. Meanwhile, whisk the dashi, eggs, mirin and tamari together in a bowl and strain through a chinois into a pitcher. Pour the custard base into the cups about ¾ of the way up. Cover with foil and place in steamer. This part is tricky because the cooking time will depend on size of your vessel. After 5 minutes, check to see if the custard is set by removing the foil and giving the vessel a gentle shake. It should wiggle a bit and when you tip the cup on its side, the custard should not pour out.
For the glaze, combine the dashi and tamari in a small sauce pot and bring to a boil. Meanwhile, in a small bowl mix the kudzu and water until smooth. When the dashi and tamari mixture is at a boil, slowly pour the kudzu slurry in a thin stream while whisking to combine. Return to boil to enable the kudzu to thicken the mixture. Taste for seasoning, then lightly pour on top of each chawan. Note: You could use a vegetable, protein or whatever else you desire in the glaze to lightly warm it before placing on top of the chawan. Serve immediately.