Preheat the oven to 180°C.
Pierce the lamb leg 12 times and insert lavender sprigs into the holes.
Fill a deep roasting tray with hay and sprinkle with remaining lavender.
Place the lamb on the hay, rub with 50g butter, and season with salt and pepper.
Cover with foil and roast for 2 to 3 hours until cooked, then rest for 30 minutes.
Boil potatoes in salted water for 2 minutes, then drain and shake to fluff.
Roast potatoes in beef dripping for 50 to 60 minutes until golden and crisp.
Simmer vinegar and sugar, then stir in chopped mint and a pinch of salt.
Boil broccoli for 3 minutes, then drain and season with salt, pepper, and butter.
Carve the lamb and serve with potatoes, broccoli, and mint sauce.