Slash the skin side of two duck breasts, sprinkle with sea salt, then roast in a very hot oven, skin-side up, for 20 minutes. Meanwhile, for the sauce, take a tablespoon of duck fat from the roasting tin, then fry a large, chopped shallot until softened. Add 2 tbsp orange liqueur (such as Grand Marnier or Cointreau) and 3 tbsp red wine to the pan, let it bubble for a few seconds, then add the juice of an orange and 3 tbsp water. Stir in 2 tbsp good-quality orange marmalade and a sprinkle of orange zest. If you prefer a thick sauce, mix 1 tsp cornflour with a little water, add it to the pan, then stir until thickened. Serve with roast potatoes, with the sauce poured around the duck breasts.