I had the same problem Berkley. Having had difficulty with carrots in the open ground in the past, I sowed Early Nantes in deep troughs. They have been regularly (and copiously) watered, especially during hot, dry weather. So exactly what the problem is, I don't know - but the roots that have a hard core have the hard centre cut out. The rest of them, some not as large as I would have liked, are just scrubbed, topped and tailed and quickly steamed. Had some for dinner today (roast lamb, with fresh mint sauce and French and runner beans from the garden: delicious) and the flavour was superb, even if the odd shapes of some of the carrots would have been frowned on by the MasterChef judges! But then - I grow for taste not presentation.