In a bowl, whisk the Eggs together with the Dashi, Mirin, Soy Sauce, Sugar and a pinch of Salt until the mixture is smooth and lightly frothy; for the silkiest texture, strain the mixture through a fine sieve.
Heat a rectangular tamagoyaki pan or a small nonstick skillet over medium–low heat and lightly coat the surface with Neutral Oil (use a paper towel to spread a thin, even film).
Pour a thin layer of the egg mixture into the pan so it just covers the bottom. Tilt the pan to spread the egg evenly and cook until the edges are set but the surface is still slightly glossy.
Using a spatula or chopsticks, gently roll the set egg away from you toward the far side of the pan to form the first roll, leaving the rolled portion at the back.
Brush the pan with a little more oil, pour another thin layer of egg into the empty space, lifting the existing roll so the new egg flows underneath; when this layer is mostly set, roll the existing roll forward to incorporate it.
Repeat the oiling, pouring, and rolling process until all the egg mixture is used, keeping the heat moderate so the layers set without browning too much and rolling each new layer tightly around the previous ones.
When finished, transfer the rolled omelette to a cutting board, let it rest for a minute to set, then slice into even pieces. Serve warm or at room temperature.
