Creating the Japanese Egg Sandwich is straightforward and can be done in just a few easy steps:

1. Boil the Eggs: Place the eggs in a pot and cover them with cold water. Bring to a boil, then cover and remove from heat. Let the eggs sit for 10-12 minutes.
2. Cool the Eggs: After the eggs are done, transfer them to an ice bath or run them under cold water to cool.
3. Peel the Eggs: Once cooled, peel the eggs and place them in a bowl.
4. Mash the Eggs: Using a fork, mash the eggs until they reach your desired consistency—smooth or slightly chunky.
5. Mix Filling: Add mayonnaise, Dijon mustard (if using), salt, and pepper to the mashed eggs. Mix until well combined. Add chives or green onions if desired.
6. Prepare the Bread: Take two slices of Japanese milk bread and spread a thin layer of mayonnaise on one side of each slice.
7. Assemble the Sandwich: Spoon the egg mixture evenly onto one slice of bread. Top with the other slice, mayo side down.
8. Cut the Sandwich: Cut the sandwich in half or into quarters for easier handling.
9. Serve: Enjoy your delicious Japanese Egg Sandwich immediately or pack it for later.

These steps will guide you in creating this incredible sandwich effortlessly.