3 1⁄2 pounds Kennebec potatoes Sea salt and pepper
1⁄2 tsp baking soda
6 tbsp duck fat
1 tbsp chopped fresh rosemary
1. Adjust oven rack to top position, place rimmed baking sheet on rack, and heat oven to 475 degrees.
2. Bring 10 cups water to boil in Dutch oven over high heat. Add potatoes, 1/3 cup salt, and baking soda. Return to boil and cook for 1 minute. Drain potatoes. Return potatoes to pot and place over low heat. Cook, shaking pot occasionally, until surface moisture has evaporated, about 2 minutes. Remove from heat. Add 5 tablespoons fat and 1 teaspoon salt; mix with rubber spatula until potatoes are coated with thick paste, about 30 seconds.
3. Remove sheet from oven, transfer potatoes to sheet, and spread into even layer. Roast for 15 minutes.
4. Remove sheet from oven. Using thin, sharp, metal spatula, turn potatoes. Roast until golden brown, 12 to 15 minutes. While potatoes roast, combine rosemary and remaining 1 tablespoon fat in bowl.
5. Remove sheet from oven. Spoon rosemary-fat mixture over potatoes and turn again. Continue to roast until potatoes are well browned and rosemary is fragrant, 3 to 5 minutes. Season with salt and pepper to taste. Serve immediately.
Saving Fat for Cooking
Saving the leftover fat from duck is easy to do. Pour the warm fat through a fine-mesh strainer into a Mason jar and discard any solids.
Alternatively, let the fat cool and harden and then scoop it into the jar, leaving any solids behind.
Put the lid on the jar, label it, and refrigerate it for up to one month or freeze it for up to six months, adding more fat as desired.