Dry the duck legs well and put them in a glass baking dish with enough room for them to lay side by side (no overlapping). In a small bowl, mix together the salt, thyme, pepper and fennel seed. Sprinkle the mixture on both sides of the duck legs, lightly pressing it into the skin and meat.

Place in the refrigerator, uncovered, for 24 - 48 hours hours to let the skin dry and cure. (They will look weird and wrinkly but don’t panic, that’s what makes them crispy).

When you’re ready to cook, pre-heat oven to 325 F.

Heat a large, heavy-bottomed skillet or sauté pan on medium high and add the duck legs in a single layer skin side down (no need to add any oil). Press down to make sure you have good contact between the skin and the pan. Cook until the skin is deep golden brown (8-10 minutes). Turn them over and brown the meat side (5 minutes longer). If your pan isn't large enough to do this in a single layer, cook them in batches. Don't rush this step because the fat that is rendered at this point will help the legs cook in the oven.

If you've cooked the legs in batches, transfer the legs and all the rendered fat to a large roasting pan, arranging the legs skin side up in a single layer. (If they fit in the single pan, just leave them, skin side up, and all the rendered fat, in the skillet). Cover the pan with aluminum foil and place in the oven. Cook for 1 1/2 hours.

Remove the pan from the oven, and remove the legs to a large plate or sheet pan. Drain the fat out of the roasting pan (be careful -- it's hot) into a heatproof bowl, leaving about 1 tablespoon of fat in the pan. Return the legs to the roasting pan, again skin side up, uncovered. (Alternately, you could use a turkey baster to siphon out the fat).

Turn the oven up to 350F and return the uncovered pan to the oven for 30 more minutes until the skin is crispy.