Heat sunflower oil in a small frying pan over medium heat.
Fry sage leaves for 30 seconds until translucent, then drain on kitchen paper.
Peel and cut carrots, parsnip, and celeriac into 2.5cm chunks.
Boil the vegetables in a large saucepan for 30 minutes until tender.
Drain and mash vegetables with 50g butter, nutmeg, salt, and pepper.
Sauté sliced onions in 25g butter for 14 minutes until golden-brown and set aside.
Season lamb chops and fry in sunflower oil for 3 minutes on each side.
Rinse, halve, and core the lamb kidneys.
Toss kidneys in seasoned plain flour and shake off excess.
Sear the fat edge of the lamb and add kidneys to the pan for 3 minutes.
Rest the lamb while cooking kidneys for 3 more minutes until browned.
Deglaze the pan with Marsala, adding onions and remaining 25g butter to thicken.
Serve lamb and kidneys with sauce, sage, mash, and green beans.