Heat the oven to 230C/450F/gas mark 8. Wash and trim the carrots, leaving just a centimetre or two of stem on each, then peel. You want 10cm-long and 1.5cm thin pieces of carrot, so, depending on their size, leave them whole, or cut them lengthways in half or even quarters, to the required size.
In a large bowl, combine the cumin, honey, harissa, butter, oil and three-quarters of a teaspoon of salt, mix in the carrots to coat and spread out on a large oven tray lined with baking paper; don’t crowd them, so use two trays if need be.
Roast for 12-14 minutes, until the carrots begin to brown but still retain a bite. Remove from the oven and leave to cool. Mix in the remaining ingredients and serve.
