How to Make It
In a medium bowl, whisk the eggs with the mirin, soy sauce and salt.
Brush a 10-inch nonstick skillet with oil. Add one-third of the eggs and swirl the skillet to evenly coat. Cook over moderate heat until the egg is almost set, about 1 minute. Using a spatula, roll up the omelet and push it to the side of the skillet. Brush the skillet with more oil, then add another one-third of the eggs, lifting the rolled omelet so the uncooked egg flows underneath it. Cook until the egg is almost set, about 1 minute. Roll up the first omelet in the cooked egg, forming a second layer; push to the side of the skillet. Repeat this process one more time with more oil and the remaining eggs. Turn out the omelet onto a work surface and slice 1 inch thick. Serve warm.