Heat oven to 190C/170C fan/gas 5.
To make the stuffing, mix together all
the ingredients, except the butter, in a
large bowl with some seasoning. Scrunch
with your hands until well combined.
Season the chicken all over and put
in a roasting tin. Smear with the butter
and put on the middle shelf of the oven
for 50 mins.
Meanwhile, grease a 20 x 30cm
roasting tin. Press in the stuffing, then
sprinkle with the reserved breadcrumbs
and dot with the butter.
Brush the chicken with the mustard,
transfer it to a lower shelf and roast for
40 mins more until cooked through and
the juices run clear. Put the stuffing
on the top shelf at the same time and
cook for 40-50 mins until golden and crisp.
Leave the chicken to rest for 10 mins,
then serve with the stuffing, along with
roast potatoes and veg, if you like.