Remove the veal shank from the refrigerator half an hour before cooking and pat it dry. Tie a piece of kitchen twine tightly around the edge, as the surrounding membrane contracts in the oven and would otherwise warp the shank and push it off the bone.
Season the meat generously with salt and pepper. Heat two tablespoons of olive oil in a cast-iron pan until almost smoking, and sear the shank for three to four minutes per side until a deep brown crust forms. Take your time here: this crust is the flavor foundation of the entire gravy and only develops with dry meat in a hot pan.
Remove the meat and sauté the finely chopped onion, carrot, and celery in the remaining olive oil for eight minutes until soft. Add the garlic and cook for another half a minute. Deglaze the pan with the white wine, scraping up the browned bits from the bottom, and let it reduce by half.
Add the diced tomatoes, stock, bay leaves, and thyme, and return the shank to the pan. Cover and braise in the oven at 160 degrees or over very low heat for two hours, until the meat is fall-off-the-bone tender.
Boil the cauliflower for ten minutes until soft, drain well and let the steam escape, then purée with the butter and cream. Serve with lemon zest and parsley sprinkled over the shank.