Creamy Japanese Egg Sandwich

Instructions:

1. Place eggs in a saucepan and cover with cold water. Bring to a boil, then immediately remove from heat and cover with a lid. Let sit for 12 minutes.
2. Plunge the eggs into an ice bath for 5 minutes to stop the cooking process, then peel.
3. Separate the yolks from the whites. Mash the yolks in a bowl with the sugar, salt, and white pepper until a smooth paste forms.
4. Stir in the Kewpie mayonnaise until the mixture is glossy and uniform.
5. Finely chop the egg whites and fold them gently into the yolk mixture.
6. Spread a thin, even layer of softened butter on one side of each Shokupan slice.
7. Spoon the egg mixture onto the buttered side of one slice, smoothing it to the edges, and top with the second slice, butter-side down.
8. Wrap the sandwich tightly in plastic wrap and let it rest for 5 minutes to set.
9. Use a serrated knife to trim the crusts and slice the sandwich in half.