Pre-heat the oven to 200°C.
Prepare the parsnip purée by cooking the parsnip in boiling, salted water until tender; usually 10-15 minutes. Drain and transfer to a food processor. Blitz until smooth and transfer to a mixing bowl then beat in half of the butter and some seasoning. Reserve to one side.
Prepare the herb oil by blitzing together the herbs and the olive oil in a food processor until you have green oil, transfer to a jug, cover, then reserve to one side until needed. Season the best ends of lamb then heat an oven-proof frying pan over a medium-high heat until hot. Sear the best ends of lambs until some of the fat has rendered down and the meat is golden on the ends and the underside. Roast in the oven for 8-10 minutes.
Meanwhile, brush the mushrooms lightly to clean them, then melt the remaining butter in a large frying pan and saute the mushrooms over a medium-high heat with a little seasoning for 2-3 minutes until just soft.
Remove the lamb and allow it to rest for a few minutes before carving into chops. Re-heat the parsnip purée in the microwave until piping hot. Arrange the lamb chops stacked on plates and spoon the herb oil over the top. Place a tablespoon of the mushrooms and some parsnip purée beside the lamb before garnishing with a sprig of chervil and serving.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.