Prepare the Egg Mixture: In a bowl, beat the eggs thoroughly. Add sugar, soy sauce, mirin, and salt to the eggs, and whisk until well combined.
Cook the Tamagoyaki: Heat a non-stick or tamago pan over medium heat and lightly grease it with oil. Pour a thin layer of the egg mixture into the pan, tilting it so the egg spreads evenly. Once the egg is partially cooked but still slightly runny on top, start rolling the egg from one side to the other using chopsticks or a spatula. Move the rolled egg to one side of the pan, grease the pan again, and pour another thin layer of the egg mixture. Once this layer is partially cooked, roll the previous roll back over it, and continue the process until all the egg mixture is used and you have a thick roll.
Serve: Once done, remove the tamagoyaki from the pan and let it cool slightly. Slice into thick pieces and serve with soy sauce or as part of a bento.
