Preheat the oven to 200 degrees Celsius (390 Fahrenheit).
In a frying pan set over a medium heat, melt the butter, add the peeled and chopped onion, and fry until golden.
Add the seasoning and herbs and give it a good stir.
Add the bread slices to a food processor, and blitz until you get breadcrumbs.
Remove the breadcrumbs and blitz the chestnuts too to a similar texture.
In a large bowl, add the breadcrumbs, chestnuts, cranberries, onion mixture and beaten egg.
Mix well to get a sticky paste.
With wet hands, shape 14 balls - you can get more or less depending on their size.
Line a baking tray with non-stick paper, and arrange the stuffing balls.
Spray them lightly with cooking oil spray and bake for 25 minutes or until golden.