Making Japanese Tamago Sando involves only a few simple steps. Follow these easy instructions to create your delicious egg sandwich:

1. Boil the Eggs: Place the eggs in a saucepan and cover them with cold water. Bring to a gentle boil and cook for 9-10 minutes for hard-boiled eggs.
2. Prepare the Ice Bath: While the eggs are boiling, fill a bowl with ice water. Once the eggs are done, transfer them immediately to the ice bath to stop the cooking process.
3. Peel the Eggs: After 5 minutes in the ice bath, peel the eggs and set them aside.
4. Mash the Eggs: In a mixing bowl, use a fork to mash the peeled eggs until they reach your desired texture, whether chunky or smooth.
5. Mix the Filling: Add the mayonnaise, Dijon mustard (if using), salt, and pepper to the mashed eggs. Stir until well combined and adjust seasoning as needed.
6. Prepare the Bread: If desired, lightly butter the slices of bread for added flavor.
7. Assemble the Sandwich: Spread a generous amount of the egg filling onto two slices of bread. Place the remaining slices on top to form sandwiches.
8. Cut and Serve: Trim the crusts off the sandwiches if you prefer a clean presentation. Cut them in half or quarters, as desired.