The chillies set the heat, and the pith and seeds carry it. Leave everything in for a properly hot sauce, deseed half for medium, deseed the lot for warm and aromatic. Taste a raw piece first: chillies vary enormously even from the same plant.
Overnight marinade. Half an hour seasons the surface; overnight gets it into the meat. It is the biggest single improvement you can make to this dish.
Cuts. Written for breast, but better on the bone. Thighs or drumsticks want 30 to 35 minutes in a hot oven; a spatchcocked bird about 45 minutes at 200C.
On 72C. That is with a five-minute rest, which is a recognised time-and-temperature combination. If you prefer the simpler official single reading, the FSA figure is 75C. Use a probe: peri peri chicken goes dark outside long before it is done inside.
The sauce keeps a month in a sterilised jar in the fridge, so make the full batch.
The seasoning is not just for chicken. Chips, roast potatoes, prawns, corn, halloumi, popcorn. Stir it into mayo or soft butter for a quick dip.