Place the peppers and red onion on a baking tray. Drizzle on 2 tbsp of the vegetable oil. Sprinkle on the paprika, smoked paprika, cayenne pepper and 1 tsp of the salt and toss together.
Place in the oven for 20 minutes.
Add the garlic and serrano chillies and toss together again, then place in the oven for a further 10 minutes.
Remove from the oven and transfer to a blender (make sure you pour in all the juices from the tray). Add the dried chillies, white pepper, lemon zest and juice and the dried rosemary. Blend until smooth.
Add the remaining vegetable oil and the red wine vinegar and blend again.
Now it's time to spatchcock the chicken. Place chicken breast-side down on a sturdy chopping board, with the legs towards you.
Using heavy-duty scissors or poultry shears, cut along both sides of the backbone. It's a little fiddly, as you have to cut through each of the rib bones as you go. So it's better to go slowly, rather than trying to cut through multiple ribs at once.
Once you've cut through both sides of the backbone, discard the bone (or save it to make stock). Turn the chicken over and press down with both hands on the breast bone to flatten the chicken.
Place the spatch-cocked chicken on a baking tray and pour over one third of the sauce. Sprinkle with the remaining ½ tsp salt and the black pepper.
Place in the oven (still at 180C/350F) for 45 minutes.
After 45 minutes, baste the chicken and spoon over 2 more tablespoons of the sauce. Place back in the oven for a further 10-15 minutes until the chicken is cooked through.
Remove from the oven and allow to rest for 10 minutes.
Serve with the remaining sauce.
Can I make it gluten free?
Yes, this recipe is naturally gluten free. However, it's always best to check your ingredients, as some brands may use wheat/barley in their products (i.e in certain types of vinegar) or packing environments.
How long will peri peri sauce keep?
Covered and refrigerated, this peri-peri sauce should keep for 2 weeks.
Nutritional Information is per serving - including one-quarter of the peri peri sauce per person.