Preheat the oven to 200°C/400ºF/gas 6. Trim, peel and halve the carrots, then scrub the beets clean, and chop into wedges. Parboil the carrots in a large pan of boiling salted water for 5 minutes, then transfer them to a colander using a slotted spoon. Carefully lower in the beets and parboil for 5 minutes, then drain (parboiling separately will stop the carrots from turning purple). Transfer the carrots and beets to a large roasting tin, drizzle with olive oil and season with sea salt and black pepper. Roast for 30 to 40 minutes, or until sticky and shiny, jiggling the tray occasionally for even cooking. Meanwhile, finely grate the orange zest. Trim off the skin and pith, then cut the orange into segments. Toast the sesame seeds in a dry pan on a low heat for a couple of minutes or until golden, tossing regularly. Pick and roughly chop the coriander leaves. When the time's up, let the roasted veg cool a little, then toss with the orange zest and segments, a good lug of extra virgin olive oil and a little extra seasoning, if needed. Arrange over a large platter, scatter over the toasted sesame seeds and coriander leaves, then tuck in.