Season the pork steaks with plenty of pepper. Heat the oil in a nonstick frying pan, add the pork steaks and fry for 2 minutes on each side until browned, then transfer to an ovenproof dish.
Mix together the cheese, sage, breadcrumbs and egg yolk. Divide the mixture into four and use to top each of the pork steaks, pressing down gently. Cook in a preheated oven, 200°C (400°F), Gas Mark 6, for 12–15 minutes until the topping is golden.
Meanwhile, make the purée. Place the parsnips and garlic in a saucepan of boiling water and cook for 10–12 minutes until tender.
Drain and mash with the crème fraîche and plenty of pepper. Serve with the pork steaks and some steamed green beans or cabbage.