Place the duck legs skin side down in the coarse sea salt and leave for 15 minutes. Scrape off the sea salt and place the legs into a ceramic dish with freshly ground black pepper, one crushed garlic clove, four sprigs of thyme and the bay leaves. Pack tightly into a ceramic dish, skin side down, then cover with a mixture of vegetable and olive oils, cover the dish with cling film and leave to marinate in the fridge for 24 hours.
Preheat the oven to 150°C (300°F/Gas 2).
Scrape the marinade off the duck pieces.
Heat the duck or goose fat in a heavy ovenproof casserole dish, then add the duck, the remaining garlic cloves and the remaining thyme. Make sure that the duck is completely submerged in the melted fat.
Transfer the dish to the oven and bake for 3½-4 hours, or until the meat is very tender when pierced with a skewer and the fat in the skin is completely rendered.
Remove from the oven and allow to cool uncovered. Strain half of the fat and bring to the boil in another pan, then pour into a clean ceramic dish large enough to hold the duck without it touching the sides. Leave to set in the fridge.
Once the duck is cool, place into the prepared ceramic dish and strain over the remainder of the melted fat and place into the fridge for 1-2 hours to set. (This can be stored in the fridge for up to one month.)
Preheat the oven to 200°C (390°F/Gas 6).
Scrape off the fat from the duck legs, then place into a roasting tray. Sprinkle over the coarse sea salt and roast in the oven for 40 minutes, or until the skin is crisp and golden-brown. Serve immediately.
Cook the white beans in stock until softened, add the chorizo and allow to simmer. Use a blender to puree the white bean and chorizo until smooth. Layer the potato mash and bean/chorizo puree using a mould.
For the Sauce:
Put 1ltr of stock into a saucepan, bring to the boil and allow to simmer until it reduces significantly. Add 1/4ltr of port and allow the sauce to reduce until it has thickened and the flavour has become intensive. Add seasoning to taste.