1. Mix sugar, flour, and salt with a mixer on low speed. Add lemon and orange juices, and beat until just combined. Slowly pour in butter, then increase speed to medium. Add lemon and orange zests, and continue to beat until combined. Cover, and refrigerate overnight (or up to 1 week).

2. Preheat oven to 350 degrees. Spoon batter, 1 teaspoon for each cookie, onto a baking sheet lined with a nonstick baking mat, spacing mounds at least 2 inches apart. (Refrigerate remaining batter between batches.) Using a small offset spatula, spread mounds into 3-inch circles. Bake cookies until uniformly light gold, 10 to 12 minutes. Let cool on baking sheet for 1 minute. Working quickly, flip cookies over, smooth side up, and roll each around the handle of a wooden spoon. Let stand until hardened. (If cookies become too difficult to roll, return to oven until warm and flexible.) Repeat with remaining batter. Rolled cookies will keep, layered between parchment and covered, for up to 3 days.