Let's cook.
In a medium bowl, whisk together the eggs, dashi stock (or water), sugar, soy sauce, and salt until just combined. Do not over-whisk; you want to avoid too much foam.
Heat a non-stick rectangular tamagoyaki pan or a small non-stick skillet over medium-low heat. Lightly coat the pan with a small amount of vegetable oil using a paper towel.
Pour about one-quarter of the egg mixture into the hot pan, tilting to evenly coat the bottom. Cook for 1-2 minutes until the edges are set but the center is still slightly runny.
Using a spatula, carefully roll the cooked egg layer from one end of the pan to the other. Push the rolled egg to one side of the pan.
Lightly re-oil the empty part of the pan if needed. Pour another quarter of the egg mixture into the pan, lifting the previously rolled egg slightly so the new mixture flows underneath it.
Cook for another 1-2 minutes until the new layer is mostly set. Roll the entire omelet (including the previous layers) from the side with the cooked egg towards the other side.
Repeat steps 5 and 6 with the remaining egg mixture until all the egg is cooked and rolled into a multi-layered omelet.
Remove the tamagoyaki from the pan and place it on a cutting board. Let it rest for 1-2 minutes, then slice into 1-inch thick pieces and serve warm.
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