Preheat the oven to 200°C.
Pierce the lamb leg eight times and insert a garlic clove, rosemary sprig, and thyme sprig into each hole.
Brush the meat with pesto, season with salt and pepper, place in a tray, and drizzle with oil.
Roast for 45 to 60 minutes until cooked to your preference.
Cover the lamb with foil and let it rest for 20 minutes.
Boil 2 litres of water in a large pan.
Add potatoes, bouillon, salt, thyme, mint sprig, bay leaves, and halved garlic heads to the boiling water.
Drain the potatoes and discard the herbs, garlic, and liquid once tender.
Toss the potatoes with butter, chopped mint, salt, and pepper.
Carve the lamb and serve on plates with the prepared new potatoes.