Pan fry the lamb rump in a hot pan with the butter, oil and rosemary. When coloured, flip over and repeat, season, and pop in the oven for 15 minutes.
Take the meat out to rest for 6 minutes.
In another pan, heat the butter with the water, pop in all the vegetables and boil rapidly for 2 minutes, and season..
Spoon the vegetables onto a plate, slice the lamb and place on top.
Preheat the oven to 170C
Place the onions and halved garlic into a roasting tray, and top it with the lamb. Season well and pour in the wine, stock and thyme rosemary. Cook in the oven for two hours.
Pop the meat, onions and garlic onto a board to rest. Reduce the leftover liquid down by half and add a knob of butter.