Potato salad is not really Japanese or Izakaya food, yet, it is definitely very common home cooked food in Japan. Last time we were in one of our favarite Izakayas in Kyoto, "Akagakiya" 赤垣屋, the first appetizer or "Otoshi" おとうし was potato salad which was excellent. There is always something different from usual American-style potato salad in Japanese versions. Mark's book has a rather sophisticated version of potato salad (p81). One of more common Japanese variations is called "taramo" which is a made-up word from "tara-ko" (cod roe) and "imo" (potato). I made my variation of "taramo" salad since I had "tarako" I did not use after making other dishes. I added black olive, finely sliced French Cornichons (tiny cucumbers, gherkins, pickled in a tangy marinade), and instead of using just mayonnaise, I used an equal mixture of plain yogurt and mayonnaise, which is bit better fat-wise and also add a slighly sour tangy flavor to the dish. An addition of yogurt, however, makes the salad a bit watery, so it is important to use white potatoes and cook them whole and remove the skin before mashing to make sure the potato is rather dry to begin with.
I used two large white potatoes which were boiled in salted water whole (you could microwave, also) until a skewer goes through easily. Remove skin using a towel and mash with 1 tbs of butter and a pinch of salt (be light on salt since "tarako" is also salty) and let it cool to a room temperature. Meanwhile I remove the pits from 7-8 black oil cured olives (I am not sure which kind we got here from a local gourmet grocery store) and coarsely chop. I usually use thinly sliced fresh cucumbers (salted and then vinegared) but the mini-cucumbers we got this time did not taste particularly good, so I used pickled French Cornichons finely sliced (4-5). Add 2 tbs each of mayonnaise and plain yogurt and one large sac of tarako (which was removed from the sac and mixed with 1 tsp of lemon juice and 1/2 tsp of sake). Taste and adjust the seasoning (salt and pepper). This "taramo" salad tastes better after leaving it overnight in the refrigerator (especially the textures improves).
Please note that the size of Cornichons I used for a garnish is only 1 inch in length and the tomato is cherry tomato in the above picture. I served this as an "otoshi" for our Home Izakaya à la "Akagaki-ya". Although sake will be a safe choice, It went surprisingly well with an inexpensive everyday Australian Shiraz "Red Dust" 2007.