Cut the onion into 4 wedges, then peel off the outer papery layer and trim the root section. You want the onion to hold together, so do not cut off too much of the root.
Place the honey and harissa paste into a 15cm or 6" saucepan and heat it until it loosens, then stir to combine.
Heat a 25cm or 10" frying pan over a medium-high heat, and when it is hot, add the butter. Place the chicken thighs in the frying pan, skin side down, and cook until they are lightly coloured.
Flip the chicken, then squeeze in the onion wedges and cinnamon bark. Sprinkle over the salt, dried mint and sumac.
Pour the honey and harissa mix over the chicken, then spread it out using a pastry brush. Transfer to the oven and cook at 200°C or 390°F (fan mode) for 22-25 minutes. Ensure that the chicken has reached 73°C or 165°F before serving.