Unwrap the chicken. Remove the giblets (see our tip on how to use them) and put the chicken in a roasting tin. Set aside.
Pour ½ the yogurt into a bowl. Add most of the saffron powder (reserving a little pinch for later), the finely grated zest of the lemon, a squeeze of juice from ½ the lemon and a good pinch of salt. Mix together. Put the squeezed lemon half and both bay leaves in the chicken cavity. Spread the saffron yogurt all over the chicken.
Cover the whole roasting tin with foil, making sure it doesn’t touch the chicken, and set aside to let the chicken marinate for at least 30 mins at room temperature, or overnight in the fridge, if possible. If doing the latter, make sure you bring the chicken back to room temperature before cooking.
While the chicken marinates, heat your oven to 180°C/Fan 160°C/Gas 4. Keep the chicken covered and roast for 1 hr. Remove the chicken from the oven.
Turn the oven up to 220°C/Fan 200°C/Gas 7. Uncover the chicken. Return it to the oven and roast for a further 30 mins, or till golden brown and the juices run clear when the fattest part of the leg is pierced. Cook a little longer if the juices aren’t clear.
Let the chicken rest for a good 30 mins-1 hr, loosely covered with foil, before carving. Mix the remaining yogurt and saffron together. Serve the chicken with the saffron yogurt and the remaining lemon half, sliced into wedges, for squeezing.