1. Slice the cabbage as thinly as possible and set aside.
2. Place each pork steak between 2 pieces of freezer film and,using a meat mallet,flatten to about 1cm thickness. Season fillets on both sides with salt and pepper. Working one steak at a time,dredge pork with flour and shake off excess. Coat in beaten egg and crust evenly with panko.
3. Heat vegetable oil to 170°C in a heavy frypan. If you don't have a thermometer,heat the oil until a pinch of excess panko floats and turns golden brown in about 30 seconds.
4. Cook the pork in batches,without overloading your frypan,for about 4 minutes,turning once until the fillets turn golden brown. When they are ready,transfer to a paper-towel-lined plate to drain.
5. Slice the pork into 2cm-wide strips. Place each portion on a plate,along with a heap of sliced cabbage and a dab of mustard. Serve topped with about 2 tablespoons of tonkatsu sauce,steamed rice,and microcress or fresh herbs if using.