Creating the perfect Japanese Egg Sandwich is easy if you follow these simple steps:

1. Boil the Eggs: In a small pot, bring water to a boil. Gently add the eggs and boil for 8-10 minutes for hard-boiled eggs.
2. Cool and Peel: Once cooked, transfer the eggs to a bowl of ice water. Let them cool for about 5 minutes, then peel.
3. Mash the Eggs: In a bowl, roughly mash the peeled eggs with a fork, leaving some chunks for texture.
4. Add Seasonings: Mix in the mayonnaise, Dijon mustard (if using), salt, and black pepper until well combined. Adjust to taste.
5. Optional Add-ins: If desired, fold in the chopped chives or green onions for added flavor.
6. Prepare the Bread: Lay the slices of bread on a clean work surface or plate.
7. Spread the Mixture: Generously spoon the egg mixture onto two slices of bread and spread evenly.
8. Top and Cut: Place the remaining slices on top to form sandwiches, then cut them in half diagonally or into quarters.
9. Serve: Arrange the sandwiches on a plate and enjoy immediately!

These straightforward instructions will help you create a delightful Tamago Sando that will impress your taste buds.