Heat oven to 200C/180C fan/gas 6. Put the garlic, chilli, potatoes, fennel and remaining rosemary into a large roasting tin, pour over some olive oil and toss together. Season the lamb generously, then lay it on top of the veg. Roast for 45 mins until the lamb is starting to brown, then pour in the wine and stock. Continue cooking for 30 mins for rare (55C on a cooking thermometer), 35-40 mins for medium rare (60C) or 45 mins for cooked through (70C).