1. heat the oven to its highest setting.
2. in a large bowl mix the potatoes, harissa, garlic and oil with 3/4 tsp of salt and a grind of pepper
3. transfer to a large oven tray lined with grease-proof paper, and spread out as much as possible; cover tightly with foil and roast for 15 minutes
4. remove the foil and reduce the heat to 200’C/ 200’C fan/ gas 7 and roast for 20 more minutes, stirring half way through, until the potatoes are cooked and browned.
5. whisk all the sauce ingredients until smooth
6. transfer the potatoes to a serving dish and drizzle over the sauce, finish with the chives and sesame seeds