An easy to make kissaten (Japanese-style tearoom) sandwich. Since there's no need to cook, you can make these in a flash. The richness of the margarine and mayonnaise is delicious!
This is the sandwich my mother used to make when she worked at a kissaten. It's a comforting taste that I've loved since I was a child.
For a grown-up taste, try using karashi-mayonnaise (mayonnaise mixed with Japanese mustard) instead of regular mayonnaise.
Enjoy Japanese food around the world.