Preheat oven to 425°F (220°C). Use the tip of a sharp knife to make small 1/4-in. (5-mm) deep cuts every 1 in. (2.5 cm) or so, all over the lamb leg (this allows herbs and spices to flavour the meat more effectively). In a small bowl, stir together 2 tbsp (30 mL) oil, rosemary, 3 cloves minced garlic, pepper and 1 tsp (5 mL) salt. Rub all over the lamb. Place lamb on rack fitted onto roasting pan. Toss together potatoes, 2 tbsp (30 mL) lemon juice, 1 tbsp (15 mL) oil and 1/4 tsp (1 mL) salt. Arrange on the rack around the lamb.
Roast lamb 15 min. then reduce oven temperature to 375°F (190°C) and continue roasting about 1 hr., or until internal temperature registers 165°F (74°C) for well done, or until desired doneness. Transfer lamb to cutting board. Tent loosely with foil and rest 15 min.
Meanwhile, stir together chopped mint, lemon zest, parsley, cheese, pine nuts, remaining olive oil, lemon juice, garlic and salt to make mint pesto. Slice lamb and serve with pesto on the side. Garnish platter with mint sprigs and lemon wedges, if desired.
For medium-done roast, cook to internal temperature of 160°F (71°C).
Chop herbs in food processor for easy preparation.
To carve the leg of lamb, use a clean kitchen towel to grip the narrow end of the leg bone; tipping the bone on a 45-degree angle up from the chopping board, with the meaty part of the lamb leg resting on the board . Use a sharp carving knife to cut ½-in. (1-cm) thick slices in towards the bone (and against the grain of the meat). Rotate bone to carve all the way around the lamb leg.