In a pot of boiling water over medium-high heat, add all eggs and boil for 7 minutes and 30 seconds exactly.

Prep a bowl with cold water and ice. At 7 minutes and 30 seconds, remove ONE egg and place it in the ice bath for 2 minutes.

Remove the egg, peel it carefully, and set it aside.

At 9 minutes, remove the rest of the eggs from the pot and place them in the ice bath for 2 minutes.

Remove the eggs and peel them.

Take your hard-boiled eggs and slice them in half, adding them into a mixing bowl.

Use a fork to mash up the eggs into minced pieces.

Add the milk, kewpie, sugar, salt, and black pepper to the eggs and mix until combined.

Place this mixture in the fridge for 10 minutes to chill and thicken.

Cut the crusts from your shokupan and spread the butter on one side of each bread slice.

Cut the medium-boiled egg in half and place them face side down on two pieces of bread.

Remove your filling from the fridge and add the filling on either side of the medium-boiled egg.

Take another slice and add it on top to complete your sandwich. Repeat with the other sandwich.

Carefully slice the sandwich in half. Serve immediately.