Pre-heat the oven to 200°C/Fan 180°C/Gas 6.
Pat the skin of the duck with kitchen paper. Make parallel cuts in the skin, taking care not to cut through into the flesh.
Grate the zest of ¼ of an orange and squeeze the juice from both oranges – you need 150ml.
Put the duck breasts skin-side down in a cold frying pan. Cook over a medium heat for 5 minutes until the skin is golden brown and starting to crisp, and a lot of fat has run out. Drain off the fat and reserve. Turn the breasts over and cook the other side for 1 minute.
Transfer to a roasting tin, skin side up, and cook in the oven for 9-15 minutes, depending on how pink you like your duck. Leave to rest for 10 minutes.
Cook the shallot in 1 tbsp of duck fat until soft. Remove from the heat, add the flour then stir over a low heat for 1 minute. Gradually stir in the stock and orange juice and zest. Simmer for 3-4 minutes.
Add the marmalade and simmer until it melts. Serve the sauce with the duck, green beans and roast potatoes.