Preheat oven to 300°F. Prick duck or goose legs skin all over with a pin or sharp toothpick—this will help the fat render. Sprinkle salt all over the legs.

In a cold, 8-inch cast-iron skillet, place legs skin-side down first. Turn stove to medium and cook until the skin turns golden and some of the fat has rendered then flip legs to the meat side. A lot of fat will render out with really fatty wild duck, goose, or domestic bird legs. You should end up with enough grease to submerge the exposed meat side. If not, add more duck fat or olive oil to make up for it. The leaner the legs, the more fat you’ll need to prevent the meat from drying out.

Add cut potatoes into the pan in the empty areas around the duck, sprinkle with salt and minced rosemary, and toss in the fat to coat. Roast in a 300°F oven for 1 hour and 30 minutes, or until duck becomes tender. Flip the potatoes halfway through. Serve duck with potatoes and your favorite vegetables. The remaining rendered duck fat should be strained and refrigerated for other uses.