I saw this recipe on line. According to the recipe, this was invented by a side-dish store (called "Sozai-ya" 惣菜屋 ) of Kumamoto city 熊本市 on Kushu Island 九州, the southern most island of Japan. It was invented as a way to use up an excess amount of potato salad. Since I had frozen "chikuwa 竹輪" fish cake and leftover potato salad, I made this one weekend. The original recipe calls for chopped boiled eggs in the potato salad but I just used my usual potato salad which included myouga 茗荷 in sweet vinegar (home grown, harvested and made) and rakyo ラッキョウ, Japanese cocktail onion in sweet vinegar (store bought).
The recipe suggested tartar sauce or "chu-nou" sauce 中濃ソース but I only had "tonakatsu sauce".
Three "chikuwa"fish cakes (frozen, I had one open package with three left), thawed (#1).
Potato salad (enough to stuff the three chikuwa (#3)
Oil for deep frying
Tempura batter (3 tbs of cake flour and about 1/3 cup cold water or additional water as needed to obtain the appropriate thickness of the batter).
Slit open the sides of the chikuwa along the length (#2).
Stuff the opening with the potato salad (#3) (over stuffing is recommended to get the right ratio of fish cake to potato salad).
Dredge in the tempura batter and deep fry until the crust is done and crispy (#4). Do not over fry since the fish cake may expand.
Drain the oil (#5).
Cut on bias into two pieces and serve (#6).
This is a good combination. I served this with skinned Campari tomato and baby arugula. The center was still cold (which was good). This is definitely a nice snack. After we ate one each, we went back to finish off the third and last one.