1 For the lamb: season lamb with salt and pepper. Heat olive oil in a pan and sear meat on both sides.
2 For the cheese crust: heat butter in a pan and saute leeks until soft, dust with flour and mix well. Add sour cream and bring to a boil. Remove from heat and add sage, beaten egg white and cheese. Season with salt and pepper to taste.
3 For the sauce: saute onion in the meat drippings. Add root vegetables and saute briefly. Dust with flour, deglaze pan with broth and season with salt and pepper, simmer for about 5 minutes. Remove from the heat and add crème fraiche.
4 Spread cheese mixture on top of lamb chops and brown lightly under a hot broiler, watching carefully. Serve accompanied by the sauce.