If you are in Japan, you can find Japanese egg salad sandwiches pretty much everywhere! The most common places are bakeries, coffee shops, and convenience stores (called konbini in Japanese) such as 7 Eleven, Lawson, or Family Mart.
Japanese egg sandwich, called tamago sando (たまごサンド), is a no-frills egg salad sandwich made with Japanese milk bread, butter, and egg salad. It’s a very popular snack or lunch item because of its simplicity and convenience. It’s more basic than the American version which is served on different types of bread and have other ingredients as toppings.
Mash eggs in a bowl using a fork.
Add all ingredients to eggs except butter and continue mashing.
Spread butter on slices of bread then spread egg salad and top with remaining slices. Cut in half and serve!