1. Preheat the oven to 200C/400F/gas mark 6. Cut one of the apples into quarters, remove the core and stuff 2 quarters into each bird cavity. Peel, core and roughly chop the other apple.
2. Heat half of the butter in a saucepan and gently fry the onions until soft and transparent but with no colour.
3. Add the apple, cover and cook for another 5 minutes.
4. Add the port and bring to the boil.
5. Pour the port and apple mixture into the base of a small roasting tin fitted with a rack and place the partridge on top. Smear the breasts with the rest of the butter.
6. Roast for 25-30 minutes, basting once or twice with the sauce. Remove from the oven and let the birds rest while you finish the sauce.
7. Pour the sauce into a blender or food processor (or use a hand blender) and process until smooth. Pass through a sieve, taste for seasoning, adding salt and pepper if necessary and serve separately with the partridge.
Serve with cabbage braised in a little apple juice.