• Place the eggs in a saucepan and add enough cold water to cover them by about 2.5 cm (1 in.).
  3 large eggs
  
• Set the pan over medium heat and bring to a boil. Once boiling, cook for 12 minutes.
• Immediately transfer the eggs to the ice water to halt the cooking. Let them cool completely, then peel.
  1 bowl ice water
  
• Place the peeled eggs in a bowl and mash with a fork.
  
• Add the salt and sugar, then mix.
  0.25 teaspoon granulated sugar, 0.25 teaspoon fine salt
  
• Stir in the pepper.
  1 pinch freshly ground black pepper
  
• Fold in the mayonnaise until smooth. Taste and adjust the seasoning. For an even creamier filling, stir in the milk now.
  2 teaspoons whole milk, 2 tablespoons Kewpie mayonnaise
  

Assembling the Tamago Sando

• Lay out the 4 slices of shokupan and generously butter the top side of each one.
  4 slices shokupan, softened salted butter
  
• For each sandwich, spoon the egg filling onto one slice and spread evenly.
  
• Top with the second slice, buttered side down. Place the sandwiches between two plates and gently press to compact. Let sit for 5 minutes.
  
• Trim off the crusts.
  
• Cut each sandwich in half and serve immediately.