Tamago-Toji Udon (Udon Noodles with Egg Drop Soup)

Put water in a pot and bring it to a boil. Once it comes to a boil, reduce the heat to low, add the bonito flakes, and let it simmer for 2 minutes.
Turn off the heat and strain the mixture through a sieve lined with paper towels or cloth (such as cheesecloth). Bonito dashi is ready.
Peel the ginger and cut it into long, thin strips. Thinly slice the green onion.
Crack the egg into a small bowl and beat it. Mix the starch and water together in a small bowl.
Return the bonito dashi to the pot, add the shredded ginger and the seasonings (mirin, salt, light soy sauce), and bring it to a boil. Once the mixture reaches a boil, gradually add the dissolved starch to the pot, stirring to blend. Keep simmering for about 10 seconds to eliminate the powdery taste of the starch.
Gradually pour the beaten egg into the pot while ensuring even distribution. Once you are certain that the egg mixture is cooked, stir it.
When using frozen udon noodles: Lightly sprinkle water over the udon noodles. Then, place them on a microwave-safe plate, cover with plastic wrap, and microwave at 1000W for about 2 minutes.
When using fresh, dried, or pre-cooked udon noodles: Boil the udon noodles according to the package instructions and drain in a colander.
Place the udon noodles in each bowl and pour the liquid mixture (udon soup) over them. Loosen the udon noodles with chopsticks and then top with green onions.