Heat your oven to 180°C/Fan 160°C/Gas 4. Take the chicken out of the fridge, unwrap it and pop it in a roasting tin. Let it come to room temperature.
While the chicken is warming up, char the pepper. If you have a gas hob, you can set a hob to medium and lay the whole pepper directly on the flame. Char it for 15 mins, using tongs to turn it and move it around so it’s black all over. Take off the heat and pop in a bowl. Cover with cling film and leave to cool.
No gas hob? Halve the pepper, scoop out the seeds and white bits and lay on a grill pan or baking tray, cut-side down. Slide under a preheated grill for 10-15 mins till the skin is charred and bubbled. Set aside to cool.
While the pepper is charring, halve the chipotle and scrape out the seeds (they’re very spicy). Pop it in a bowl and cover with boiling water. Leave it to soak for 5 mins. Zest and juice the lime.
Peel the skin off the pepper and roughly chop it. Drain the chipotle. Put the pepper, chipotle and lime zest and juice in a small food processor with 1 tbsp sugar, 1 tbsp oil, 2 tbsp water and a pinch of salt and pepper and blitz to make a chunky paste.
No food processor? Finely chop the pepper and chipotle and mix everything together in a bowl, without the water to make a chunkier sauce.
Spoon the chipotle sauce all over the chicken and rub it in to make sure the chicken is well coated. Loosely cover the roasting tin with foil, scrunching the sides to seal it. Roast in the oven for 1 hr 15 mins, then remove the foil and roast for a further 20 mins till the chicken is golden brown and cooked through. (Pierce the thickest part of a thigh with a skewer or knife. If the juices run clear and there is no trace of pink, the chicken is ready.)
Transfer the chicken to a board, loosely cover with foil and rest for 20-30 mins before carving and serving.