Remove 8-10cm from the narrow end of the parsnip and place on a perforated tray. Peel and remove the root end from the remainder of the parsnip a grate it on the coarse side of the grater.
Place the grated parsnip into a zip lock bag with cream and salt. Seal the bag removing as much air as possible and place onto the perforated tray with the parsnip ends.
Place the parsnip into the oven steam setting 100 °C for 20 minutes
Season the lamb liberally with salt and place it into a zip lock bag with thyme sprigs, picked rosemary, crushed garlic and a generous splash of evoo. Seal the bag removing as much air as possible and set aside.
Once the parsnip is cooked remove the tray from the oven and re-set the oven to 60 °C steam setting.
Place the lamb in a deep-sided frypan and cover with water that is at 60 °C. Place the lamb in the oven and cook for 80 minutes.
Set the parsnip ends aside and place the grated parsnip into the jug of a blender. Blend the parsnip and add 15gm of butter while blending. Blend until smooth, check the seasoning and place the puree in a bowl and set aside.
Remove the stalk end from the brussel sprouts and peel away the leaves. Place the leaves on a perforated tray and set aside. Once the lamb is cooked remove it from the oven and re-set the oven to 100 °C steam setting.
Discard the water and dry the frypan, place the frypan over medium heat and add a splash of evoo. Pan fry the lamb on all sides until golden and crisp.
Place the brussel sprout leaves and puree into the oven to warm for 6 minutes.
Add the remaining butter to the lamb and add the parsnip ends to the pan, remove the pan from the heat and rest for 5 minutes.
Remove the butchers twine from the lamb and slice it into 2-3cm pieces. Remove the puree and brussel sprout leaves from the oven, spoon some puree onto a large serving platter and place the lamb on top of the puree.
Place the parsnip ends on the plate and scatter over the brussel sprout leaves, finish with a sprinkle of salt and drizzle of oil and serve.