Heat a medium saucepan and add the oil. Cook the onions until softened.
Stir in the flour and cook for a minute then whisk in the stock and milk.
Bring to the boil then simmer over a medium heat for about 5 minutes until thickened. Season well, stir in a teaspoon or 2 of cranberry sauce, remove from the heat and set aside.
Carefully mix the meat and veggies into the sauce then tip the whole lot into a large pie dish or steak pie ashet that will take the filling almost up to the top.