A quick search for “chawanmushi recipes” yields thousands of results that have one thing in common: vague cooking instructions.  The actual recipes themselves are more or less the same: 3 parts dashi (with mirin/soy sauce) to 1 part beaten egg, plus additional ingredients.  Steaming the mixture however, is an entirely different matter.  Most of the recipes found on the first page have vague descriptions, like steam for 10-12 minutes on medium heat.  One helpful recipe explains that low heat is important for creating silky smooth chawanmushi (doesn’t overcook, less bubbles).  The problem is that terms like medium heat, or test with toothpick means plenty of trial and error. Chances are your first few chawanmushi will turn out like this:

I won’t name the restaurant that inflicts the above dish on its diners, but let it serve as a warning: don’t let this happen to your chawanmushi!

One alternative to steaming is to cook the chawanmushi in a bain marie (water bath).  A while back, I posted on the difficulties of making soft boiled eggs given that the yolks and whites coagulate at very different temperatures.  But when used in a custard, beaten eggs coagulate at a higher temperature, about the same as egg whites.  This is in part due to the addition of extra liquids like milk or water that do not coagulate.  Since a chawanmushi is also a custard, its effective cooking temperature should be between 80-85° C.

So, you can either try and guesstimate the cooking times and temperatures for a oven-based bain marie (like in the aforementioned recipe), or if you happen to own a sous-vide machine, you’ll find making chawanmushi ridiculously easy.  I set my Sous Vide Supreme at 81° C and cooked for about 45 min for a slightly firm and silky smooth texture.  Another benefit of slow cooking and precision temperature is that it’s hard to overcook a custard.  You can leave your chawanmushi in the water bath for an hour with little noticeable change (I’ve cooked it for 4 hours, but only because I was curious).  You can also lower the temperature after cooking to keep your dishes warm until serving.

Itadakimasu!