Onsen Tamago

                                                                        

Since the point of making onsen tamago is to keep the water temperature constant for a period of time, how about:

1. using a slow cooker to cook the eggs. However, not sure what temperature the slow cooker hold on warm or low function. Need to check
2. Heat water to a little above temperature needed and pour in thermos flask. Drop the egg in and hold it there. Need to gently swirl from time to time.

Momofuku says water temp needs to be 60C or 140F. He cooks it for 40 minutes. Can't recall temp we used in Perry St. I know the time was 26 minutes. 

The FCI blog has a nice chart. All the eggs were cooked at specified temps for 1 hour.

http://www.cookingissues.com/wp-content/uploads/2011/04/The_Egg_Chart.jpg