Potato salad sandwich is very popular in Japan however I have never seen it here in America. I miss it and make at home sometimes. I love to experiment and make my American husband happy so I added bacon which makes everything perfect (according to most of people in America) and Cole slaw then deep-fried! It turned just awesome sandwich!
Peel and dice potato very small. Mince onion. Remove shell from hard-boiled egg and chop hard-boiled egg.
In a medium-large pot, cook potatoes in salted water until tender.
In the meantime, cook bacons (without oil) in a skillet until crisp. Drain on paper towels. Cut each bacon into half crosswise. Set aside.
When the potatoes are cooked, discard only hot water from the pot then put the pot back on the heat. (just potatoes are in the pot) Reduce heat to low, uncover and let the liquid evaporate shaking the pot frequently so that potatoes are not burnt. When all liquid in the pot is gone, remove the pot from the heat and transfer to a bowl. Let cool at room temperature for 10-15 minutes.
Make Cole slaw. In a bowl, mix together rice vinegar, olive oil and sugar. Add Cole slaw and mix to combine. Add salt and black pepper to taste and mix to combine. Set aside.
When the potatoes have cooled, make potato salad. Add eggs, onions, mayonnaise and Dijon mustard to the potato bowl. Add salt and black pepper to taste. Mix to combine.
Assemble sandwiches. Put the potato salad on 2 slices bread. With hands, squeeze the Cole slaw to drain and put on the potato salad. Put bacons (4 halved slices for each) and put the other 2 slices bread to close each sandwich. Press hard to seal all sides tightly.
In a bowl, whisk together all-purpose flour, water and egg. Dip all sides of sandwiches into the egg mixture then coat the all sides of sandwiches with panko.
In a fry pan, heat canola oil, put the sandwiches and deep fry sandwiches at 350 degrees F until golden brown. Turn the sandwiches and deep-fry the other side until golden brown. Drain on paper towels.
Cut each sandwich into half and place on each serving plate.