Melt 30 g of the butter in a pan and cook the onion and thyme for a few minutes without colouring.
In a bowl, mix together the minced chicken, breadcrumbs and truffle.
Add the onions, then season with salt and freshly ground pepper.
Lay the boned capon flat on a work surface then arrange the stuffing down the centre.
Roll up the bird overlapping the edges slightl