1/4 cup Dashi or Ichiban Dashi (60ml)
1 tsp soy sauce
1/4 tsp salt
1 tsp sugar
1 tsp Mirin
oil for pan
Mix all the ingredients in a bowl.
Heat a pan at medium high temperature and add oil. (A rectangular Tamagoyaki pan is best, but a round pan can work as well.)
Pour a thin layer of egg mixture in the pan, tilting to cover the bottom of the pan. After the thin egg has set a little, gently roll into a log. Start to roll when the bottom of the egg has set and there is still liquid on top. If you let the egg cook too much, it will not stick as you roll the log. Now you have a log at one end of the pan. Pour some more egg mixture to again cover the bottom of the pan, with the roll of egg at the end. After the new layer has set, roll the log back onto the the cooked thin egg and roll to the other end of the pan. (You can also keep rolling in one direction by sliding the rolled egg back to the same end of the pan before adding more egg.)
Repeat adding egg to the pan and rolling until the egg mixture is used up.
Remove the egg log from the pan onto a sushi mat, roll up lightly, and let it cool for 10 minutes.
Unwrap the sushi mat and slice the log into 1/2″ thick pieces. You should see a wavy pattern along the edge of the cross section of the egg from the mat.