To make the glaze, place the black garlic paste, sugar, rosemary and balsamic vinegar in a saucepan.  Bring to the boil and simmer for five minutes.  Strain and set aside.   Peel the kumara and boil in a large pot of salted water until tender.  Drain well and blend in food processor with butter, olive oil and milk.  Season to taste.   Trim the lamb racks, removing the silver skin from the loin, but leaving about an inch of the fat cap between the loin and the ribs.  Score the fat cap with a sharp knife and scrape any sinew from the ribs.   Preheat the oven to 200˚C.  Season the racks well with salt and pepper, then sear in a hot pan, loin side down. Turn the rack over, brush with the black garlic glaze and place in the oven for 10-12 minutes, basting ever few minutes with more glaze.  Once the racks come out of the oven, transfer them to a wire rack. Glaze a final time with black garlic and cover with tin foil.  Rest for 7-8 minutes before serving.  Serve half a rack or four ribs per person.   While the lamb is cooking, in a large pan, fry the mushrooms in the oil over a medium-high heat.  Once they have some colour, add in the shallot, garlic and butter. Cook for a further 2 minutes, then add in the roughly sliced cabbage, the asparagus and ½ of the water.  The cabbage should be just cooked and most of the liquid should evaporate.  You can add more water if needed. Finish with chopped parsley and season with salt and black pepper.  Serve immediately with the lamb and kumara mash. Garnish with peppery nasturtium leaves.   If you want to do something fun with the savoy mix, you can blanch some large nasturtium leaves, roll the mix into a ball and wrap it in the leaves, then reheat in a steamer.