Using a fork, smash the eggs coarsely, as smooth or chunky as you like.
Add the mayonnaise, mustard, sugar, salt and pepper and give a good mix.
Divide into three equal portion.
Cut each bread into half. Spread butter on both the slices. Spread the egg mixture on one slice and top with the other. Repeat with the others to get three rectangular sandwiches.
Serve immediately.
Notes
Usually Japanese mayonnaise is used. If you have in your pantry, then skip the mayonnaise, mustard and sugar, and use instead.