Duck confit should be prepared days ahead. Trim fat from legs and thighs if needed, leaving skin intact over meat. Chop the knuckle off the drumstick of the duck legs using a chef knife or cleaver. In a large pot or container, arrange duck legs flesh side up and spread coarse or grey salt all over along with the crushed garlic and fresh thyme. Cover with plastic wrap in contact and lid and chill to cure for 12 to 24 hours. Salt-curing the meat acts as a preservative. Thoroughly rinse salt from duck and discard garlic and thyme; pat dry.
Preheat conventional oven to 275°F/135ºC. Simmer duck fat and duck trimmings in large saucepan over medium-heat. Place duck in a Dutch oven or a large deep roasting pan. Pour hot fat over to cover. Seal with parchment and lid or foil; place in oven. Cook until meat is tender, about 3 hours. Uncover and leave it to rest for an additional hour on the stove top. Gently transfer legs to a wire rack to drain and refrigerate until firm. Meanwhile carefully strain the duck fat and leave it to cool until it reaches about 95ºF/35ºC. Once the duck is completely chilled, arrange legs standing up in clean containers and covered in duck fat. Duck confit can be refrigerated up to 6 weeks.
Wash potatoes thoroughly and remove any dark spots and dirt; pat dry. Cover potatoes with melted duck fat, add some thyme or rosemary and a bay leaf, and garlic bulb (Top trimmed off). Bring to a boil, cover and cook on low heat for about 25 minutes or until tender. Remove potatoes from the pan and continue roasting garlic; uncovered for 20 minutes more on low heat or until light brown color. Drain and season potatoes with salt and pepper.
Remove desired amount of confit from slightly melted fat (microwave a couple of minutes) and keeping remaining legs covered with fat. In a hot skillet, or dutch oven, add some duck fat sear the duck skin side down until skin is crisp; about 5 minutes. flip over and let cook for 2 minutes more and turn heat off. Let rest 4 minutes more, remove from pan, season with black ground pepper, a pinch of grey salt or fleur de sel. Enjoy!