Remove hens and stuffing from fridge and place hens in roasting pan.
With a spoon carefully fill hen cavities with stuffing.
Fold the skin around the open cavity over the stuffing and secure with wet toothpicks.
Drizzle with olive oil and then place hens in preheated oven at 400 in the lower part of the oven and cook for 30 minutes.
Check hens and pierce skin to remove any juices from the hens. Simply tip the roasting pan to allow the juices to flow from the hens.
Transfer hen juices to saucepan and set aside.
Return to the oven and cook for a further 30 mins.
Check hens once again, the hens should be almost done.
Again, tip roasting pan to drain hen juices and transfer to saucepan.
Move hens to the middle of the oven and cook for a further 30 minutes.
The hens should be nicely browned with crispy skins.
Tent hens with foil to keep warm.
Add chicken stock, wine and onion to reserved hen juices and place on high heat.
Reduce by one third.
Pour a small helping of gravy in the base of each plate and serve the hens on top to preserve the crispy skin.