01 -
Fill a big bowl with ice and cold water. This stops the eggs from cooking any further once you take them out.
02 -
Heat enough water in your pot so the eggs will be completely under. Bring it to a boil, carefully add the eggs, and cook for 7 minutes if you want them soft in the middle, or 10 minutes for firm yolks. Let them sit in the warm water for another minute, then move them to the ice bath for 2 minutes. Peel them while they're still warm to the touch.
03 -
Mash those peeled eggs in a bowl with a fork. Sprinkle in the sugar, pepper, and salt, mashing as you mix until the pieces are small but still noticeable. Add the Japanese mayo and, if you're using hard-boiled eggs, a splash of milk to make it smoother.
04 -
Spread the soft butter evenly on the bread slices. Scoop the egg mixture evenly onto one slice, then place the second slice on top with the buttered side facing in. Gently press the sandwich together, and slice off the crusts like you’d see in Japanese-style sandwiches.
05 -
Slice the sandwich in half, sprinkle some chives on top for flair if you like, and enjoy while it’s fresh.