Heat the oven to 220°C fan, or 240°C conventional. Put a large roasting tray in the oven while it heats.
Parboil the Wedges
Cut the potatoes into thick wedges. Add them to a large saucepan of cold salted water. Bring to the boil and simmer for 7 to 8 minutes. You want the edges just starting to soften, not fully cooked.
Steam Dry and Season
Drain the wedges and leave them in the colander for 3 to 4 minutes so the steam escapes. Tip them into a large bowl. Add the olive oil, cornflour, smoked paprika, cumin, garlic granules, fine sea salt and black pepper. Toss gently until evenly coated.
Roast Until Crisp
Carefully remove the hot tray from the oven. Spread the wedges out in a single layer. Roast for 20 minutes, then turn them and roast for another 20 to 25 minutes until crisp, golden and deeply coloured at the edges.
Make the Harissa Yoghurt
While the wedges roast, mix the Greek yoghurt, harissa paste, olive oil, lime zest, lime juice, grated garlic, chopped coriander and salt in a bowl. Taste and adjust. It should be creamy, spicy and bright.
Finish the Wedges
Pile the hot wedges onto a serving plate or platter. Spoon over some of the harissa yoghurt, then scatter with extra coriander and sliced spring onion. Serve the rest of the yoghurt on the side with lime wedges for squeezing over.
Notes
A floury potato works best here because it gives you the fluffy centre that makes wedges worth bothering with. Maris Piper is my usual pick. Waxy potatoes can still taste good, but they stay firmer and you miss that soft inside that contrasts so well with the crisp edges.Harissa paste varies wildly from jar to jar. Some are deeply smoky, some lean sharp and garlicky, some are much hotter than expected. I always taste it before stirring it into the yoghurt. Greek yoghurt is ideal because it’s thick enough to sit on the wedges rather than sliding straight to the bottom of the plate.