Mix the Badger Fursty Ferret Ale with 350ml water and pour half around the lamb with the olive oil. Roast, uncovered, for 30 minutes then turn the oven down to 180C/Fan 160C/Gas 4. Add the remaining beer and water, cover tightly with foil and return to the oven to cook for another 3 hours. Check liquid levels every hour adding a little more water if needed.