Japan has turned taking food on the road into an art form. Every train station is filled with hundreds of options for eating on the go, from self-heating bento boxes to ready-to-drink soup in a can. This recipe combines two of my personal favourites – the famous Japanese katsu-sando (cutlet sandwich) and tender Japanese fried chicken.
Place the chicken pieces in a bowl and add the soy sauce, sake and sugar. Squeeze the grated ginger between your fingers, adding the juice to the bowl and discarding the solids. Stir to coat and leave to marinate for about 5 minutes.
Place the potato flour in a large bowl and stir through a pinch of salt. Remove the chicken from the marinade with chopsticks and drop it into the flour, one piece at a time – adding the pieces one at a time stops you from pouring in too much of the marinade and prevents the chicken from sticking together. Coat the chicken in the flour, shake off any excess and set aside uncovered and out of the fridge while you heat the oil. This air-drying will create a crisper crust.
Half fill a large saucepan or wok with vegetable oil and heat to around 190°C/375°F. You may need to fry the chicken in 2 or 3 batches so that you don’t reduce the temperature of the oil too much. Deep fry the chicken for a minute. Remove the chicken to a rack and leave to rest for 30 seconds. Return the chicken to the oil and fry for 30 seconds, and then rest on the rack for 30 seconds. Transfer the chicken back into the oil for one last blast of 30 seconds and then rest on the rack for 2 minutes, seasoning with ¼ teaspoon salt.
For the seaweed mayonnaise, mix all the ingredients together until well combined. Cut the rolls in half and lightly toast them on the inside only. Fill with a little of the cabbage, watercress and onion. Add the fried chicken and mayonnaise and top with a little shichimi togarashi, if using.