Heat the oven to 180C/fan 160C/gas 4. Cut the racks into single ribs, then brown them in batches in a frying pan with a little olive oil and put them in a large casserole dish. Brown the veg in the same way and add them to the casserole along with the bay leaf, thyme and peppercorns, then season. Pour over the wine and stock, and bring to a simmer on the hob. Cover and transfer to the oven for 2 hours. Lightly brown the turnips in a little oil and stir them into the casserole, then cook for a further 45 minutes, or until the ribs are tender.