Place hanpen in a plastic bag and knead until smooth.

Crack eggs into a bowl and whisk with a hand mixer until fluffy and pale.

Add hanpen and salt and pepper to the eggs, mixing gently with a cutting motion.

Heat butter in a frying pan over low heat. Once melted, pour in the egg mixture and cook until lightly browned. Add cheese slices, cover, and cook for 3 minutes. Fold in half.