Pat the whole chicken dry and remove any gizzards. Allow it to sit out of the fridge for 1 ½ hours. Remove the backbone from the chicken, flip it over, breast side down, and push it down to crack the bone and open the chicken up. You can ask your butcher to do this if you don’t want to. Pat the chicken dry again.
Heat BBQ to maximum temperature. Add the chillies to a bowl and drizzle with olive oil and salt. Mix to combine. Grill the chillies on the BBQ for 10-12 minutes or until lightly charred and soft. Remove and let cool.
Remove the stem from the chillies and deseed (optional). Add the chillies to a blender with the remaining harissa ingredients except the butter. Blend well to create a thick paste. Season to taste.
Rub the chicken with half of the harissa paste, reserving the other half. If you can, also rub some harissa paste underneath the chicken skin. Drizzle with 1 ½ Tbsp (30ml) olive oil and season with salt.
Place the remaining harissa paste into a saucepan over medium heat and add the unsalted butter. Whisk to combine and melt the butter through the Sauce. Check seasoning and remove from heat.
Place the chicken breast side up on the hot BBQ and cook for 10 minutes. Flip the chicken and grill the breast side down for 5 minutes. Baste with harissa often. Transfer the chicken onto a baking tray that fits your BBQ and turn off one side of the BBQ. Cook the chicken on the cooler side with the lid down for 35-40 minutes or until an internal temperature of 70℃ - 158℉. Remove and allow the chicken covered in foil to rest for 5-10 minutes.
To make the spiced yogurt. Add all the ingredients into a mixing bowl and whisk together. Check seasoning and store in the fridge until ready to serve.
Spread a generous amount of the spiced yogurt on a platter. Lay over the harissa chicken and drizzle over the harissa butter sauce. Garnish with coriander and lime wedges. Dig in.