TAMAGO SANDO: How to Make the Japanese Egg Sandwich

In a bowl, combine the rice vinegar, sugar, salt, and Dijon mustard.

Add the egg yolk (use pasture-raised eggs, if possible) to the mixture and whisk vigorously.

Add the soybean oil slowly, in a thin stream, while continuing to whisk until it reaches the texture of mayonnaise.

Optionally, add a piece of kombu to the homemade mayonnaise to infuse it with Japanese mayonnaise flavor and set aside in the refrigerator.

Cook four eggs: remove one after 8 minutes in boiling water and immediately plunge into cold water. Cook the other three eggs completely, for 12 minutes, until the yolk is very firm.

Peel the eggs. Crack the shell of the 8-minute egg (soft yolk) and discard the shell, keeping the contents.

Peel the hard-boiled eggs and mash them completely in a container, leaving them roughly crumbled.

Mix the mashed eggs (both the soft yolk contents and the hard yolks and whites) with the homemade Japanese mayonnaise and a little salt until you achieve a very creamy spread.

Assemble the sandwich by spreading a generous layer of the egg spread onto a slice of Japanese-style bread (shokupan). Add another layer of spread if you desire more filling.

Cover with another slice of bread, gently press the sides of the sandwich, and wrap it tightly in plastic wrap, maintaining light pressure.

With a very sharp knife, cut the sandwich in half to finish.