Preheat the oven to 200°C.
Prick the lamb leg all over about 20 times and 2 cm deep using a sharp knife.
Stuff garlic strips and rosemary leaves into the holes and season with salt, pepper, and oil.
Place lamb on the oven rack with a tray underneath to catch fat and roast for 75 minutes.
Par-boil, drain, and roughen the edges of the potato chunks.
Transfer potatoes to the roasting tray under the lamb after 15-20 minutes of roasting.
Coat potatoes in fat and roast until golden, turning occasionally.
Process coriander, garlic, anchovies, nuts, and cheese, adding oil until a pesto forms.