For the chicken katsu, lightly pound the chicken thighs to an even thickness - you want them to be about 1 cm (½ inch) thick. Place three shallow bowls on your bench. In the first, combine the flour with 1 teaspoon of salt and a good grind of pepper. Whisk the eggs together in the second bowl, and put the breadcrumbs into the third.

Pour a 3 cm (1¼ inch) depth of oil into a large frying pan and heat to 165°C (320°F). To check the temperature without a thermometer, drop a small piece of bread into the oil - it should start frying immediately.

Dip the chicken into the seasoned flour, shaking off any excess, then into the beaten egg, allowing any excess to drip away, and finally into the breadcrumbs, pressing them into the chicken to coat it evenly.

Working in batches, fry the chicken in the hot oil for about 3 minutes each side or until lightly golden and just cooked through. Drain on paper towel.

Cut the bread rolls in half and spread with butter. Place a chicken katsu on each bottom half, then top with mayonnaise, tonkatsu and sriracha sauces, cabbage and pickled cucumber. Cover with the top halves of the rolls, slice in half and serve immediately.