Step 1

Preheat oven to 240C or 220C fan.

Step 2

Using a small knife, pierce lamb about 12 times all over, gently twisting to make a small hole. Push garlic into holes. Push half of the rosemary through centre of lamb.

Step 3

Tear remaining rosemary and place in a large bowl with potato, carrot, parsnip and 1 1/2 tbsp of the oil. Season and toss to coat. Place two-thirds of the vegetables in a single layer on a large baking tray. Arrange the remaining vegetables in a single layer in a large flameproof roasting pan. Season lamb and rub all over with remaining oil. Place in the roasting pan. Roast lamb and vegetables for 10 mins. Reduce oven to 180C or 160C fan. Roast for a further 40 mins for medium-rare or until lamb is cooked to your liking.

Step 4

Transfer lamb to a plate and cover with foil. Rest for 15 mins. Transfer vegetables to the baking tray. Increase oven to 220C or 200C fan. Roast for 15 mins or until well browned.

Step 5

Meanwhile, skim fat from the roasting pan, leaving 2 tbsp of the pan juices. Place over medium-high heat. Add the flour and cook, stirring, for 2 mins or until bubbling. Gradually add the wine, stirring and scraping the base to loosen any bits, until smooth. Bring to the boil. Gradually stir in the stock and mustard until smooth. Bring to the boil and simmer, stirring, for 2-3 mins or until thickened. Strain gravy into a jug. Stir in the mint and season.

Step 6

Untie lamb. Set aside half of the lamb and half of the carrot and parsnip (see Note). Carve remaining lamb and serve with the vegetables, drizzled with gravy.