1Preheat the oven to 220°C/425°F/Gas 7. Slice the top off each onion, about 1cm down, then trim the base so that it stands upright in a small roasting tin. Drizzle half the olive oil over and roast for 20 minutes until tender. (They can be put in the oven at the same time as the turkey.) Remove the onions from the oven and leave to cool
2While the onions are roasting, prepare the sausage stuffing. Heat the remaining oil in frying pan over a medium heat and fry the onion for 9 minutes until tender, turning the heat down slightly if the onions start to colour. Add the garlic and cook for another 1 minute. Tip the onions into a bowl and stir in the sausagemeat, breadcrumbs and herbs. Season with salt and pepper
3Turn the oven down to 180°C/350°F/Gas. 4. Take an onion and push the centre out from underneath so that it resembles a hollow ball. Repeat with the rest of the onions (you could add the finely chopped roasted onion to the sausage filling, if you like). Fill the onions with the sausage mixture and roast in the oven for another 20–25 minutes until the filling is cooked through. (Any leftover sausage stuffing can be rolled into balls and roasted at the same time.)
To take the pressure off the day, these stuffed onions can be made up to 2 days in advance and then simply wrapped in foil and reheated when needed.