Trim and peel the carrots, if necessary. If they are very small, leave whole; otherwise, cut them in half lengthways.
Remove the rind from the orange with a zester or grater and squeeze out the juice. Put both into a large saucepan, then add the butter or sunflower oil and bring to the boil over moderate heat.
Add the carrots to the saucepan, then season to taste with salt and black pepper. Bring back to the boil, reduce the heat to moderate, cover the saucepan and simmer for 10–12 minutes, shaking the pan occasionally, until the carrots are tender but not soft.
Meanwhile, put the sesame seeds into a small frying pan and dry-fry over fairly high heat for about 2 minutes, shaking the pan, until the seeds are golden.
Stir the sesame seeds into the carrots and serve.
Serve with plainly grilled chicken, lamb, veal or beef.
If baby carrots are not in season, you can use larger, older ones, but they will need to be sliced thinly.