1) Preheat the oven to 230°C, gas mark 8. 2) To make the herb crust, mix the breadcrumbs with the butter, herbs, garlic and walnuts. Keep mixing until the crumbs have soaked up all the butter. 3) Season lamb with salt and pepper. 4) Heat oil in a large heavy frying pan over moderately high heat until hot but not smoking, and then brown the fat side of the rack for a few minutes. 5) Lay the racks of lamb, fat side up, in a lightly oiled sroasting tin. 6) Pat the crumb mixture firmly and thickly onto the fat side. 7) Roast lamb for 20-30 minutes, depending on how you like it cooked. 8) If necessary, cover loosely with foil towards the end to prevent burning. 9) Let the meat rest in a warm place for 5 minutes before serving. 10) To serve, simply cut down between the cutlets.