Cook the potatoes in lightly salted boiling water for 10 minutes, until tender.
Meanwhile, mix the sage with the oil, lemon juice and honey and season with salt and pepper. Mix half the flavoured oil with the apple wedges and set aside. Brush the rest over the pork.
Grill the steaks under a preheated hot grill for 3–4 minutes on each side, until browned and cooked through. Set aside and keep warm.
Drain the potatoes, mash and beat in 40 g (1½ oz) of the butter, the milk and mustard and season to taste with salt and pepper. Keep warm.
Melt the remaining butter in a frying pan and quickly fry the apple wedges with the leek for 2–3 minutes, until golden and softened. Serve the pork with the mustard mash, apples, leek and any pork juices.