Have the ingredients ready and beat the eggs with a whisk. There should not be any whole egg whites left. Proper beating will prevent this or use a medium mesh to filter the beaten eggs over and let any non-mixed egg whites behind.
Mix the beaten eggs with the sugar, the soy sauce and the dashi.
Place the tamagoyaki pan on medium fire and apply a thin layer of vegetable oil using a brush (or a piece of paper towel)
Pour about 3 tablespoons of omelet mixture on the pan surface and ensure it covers the whole bottom in a thin layer. Push down any egg stuck on the sides and prick with a spatula or chopstick any bubbles that may form.
Let the egg mixture set in about 15-20 seconds
Then take the pan off the heat, tilt the handle down and fold the egg towards you using a wooden spatula or a pair of chopsticks
Place the pan back on the stove. Lightly brush the empty pan surface with oil, move the egg towards the end away from you and lightly brush the new open pan surface with some vegetable oil.
Then pour in about 3 tablespoons of egg mixture and lift the cooked egg so the liquid can flow underneath. Cook until the egg has set, about 35-45 seconds.
Then repeat steps 6, 7 and 8, until the omelette has reached sufficient size
Check if the omelet is golden brown on the sides, if not cook each side for a minute or two more.
Let cool slightly and slice with a sharp knife in 3/4 inch thick slices. Serve warm, unless it will be part of the bento box!
Repeat this procedure until the remaining egg mixture is finished. The above amounts of ingredients make 2 omelettes in total, serving three.