Pat the wings dry, then put them in a bowl with the bicarb, garlic powder and fine salt, and toss to coat. Arrange the wings in a single layer and not touching on a rack set over a foil-lined tray that will fit in the fridge, then chill uncovered for at least a few hours, or overnight.
When you’re ready to cook, heat the oven to 240C (220C fan)/475F/gas 9. Put the tray holding the rack of wings in the oven and roast for 40-50 minutes, turning once halfway, or until cooked through, golden and crisp.
Meanwhile, make the sauce. Mix the spring onions, ginger, green chillies and a pinch of coarse sea salt in a heatproof bowl. Put the oil in a saucepan and heat it to 170C (or when a piece of spring onion sizzles immediately when dropped in). Carefully pour the hot oil over the spring onion mixture and stir to combine. Add the sugar, soy sauce and vinegar, stir again to dissolve the sugar, then taste and adjust the seasoning as needed.
Transfer the hot wings to a platter, drizzle spring onion sauce all over the top and serve with the rest of the sauce on the side.
