Make the stuffing by blending the ingredients with 1 tsp salt in a food processor, taking care not to purée it – a little bit of crunch here and there makes it all the more satisfying. Check the seasoning by frying a tsp of the stuffing and tasting – adjust if you need to.
Put a piece of cling film on a chopping board and dollop on the stuffing, patting it out to rough circle just smaller than the surface of the breast meat to be covered. Make the layer thicker at one end, for the bottom end of the breasts where the meat is thinner – the extra thickness will help to keep it juicy and cook evenly. Cover with cling film and chill for 30 mins to set.
Heat oven to 190C/170C fan/gas 5. Pat the chicken dry all over using kitchen paper. From the neck end, push your fingers under the layer of skin on the breasts and wriggle them gently to release the skin and open up the pocket for the stuffing. Push right down – you will need to cover the entire breast meat area with the stuffing – but be careful not to tear the skin.
Make the spice rub by combining all the ingredients. Rub it generously over the chicken and inside the cavity, then insert the aromatics into the cavity. Unwrap the stuffing, halve it, then push half under the skin of each of the breasts, thin end first. Cover the chicken loosely with foil so the spices don’t burn.
Roast the chicken for 1 hr 10 mins. Mix 3 tbsp grape molasses with 1 tbsp hot water, brush over the skin, then increase oven to 220C/200C fan/gas 7 and return the chicken for 20 mins to crisp up the skin. Baste twice more with molasses at 5-min intervals. Test the chicken in the thigh and breast to make sure it is cooked – the juices should run clear. Take the cavity aromatics out of the chicken and set aside (don’t worry if you can’t get them all). Leave the chicken to rest for 45 mins somewhere warm, but don’t cover the skin so it stays crisp.
Meanwhile, pour the fat out of the roasting tin (there will be lots, which you can sieve and keep in the fridge for up to a week to use for cooking), leaving the juices behind. Add a little chicken stock and the cavity aromatics to the tin and bring to a boil, then sieve into a pan. Add the rest of the stock, simmer until reduced by half, then stir in 1 tsp grape molasses. Just before serving, add the resting juices from the chicken to the pan and bring the sauce back to the boil. Taste for seasoning and stir in the butter.