In a large bowl, using an electric mixer, cream the butter and granulated sugar together until light and fluffy. Beat in the egg, a pinch of salt, and the orange zest. Gradually mix in the flour.
Divide the dough into two portions and place each on a sheet of plastic wrap. Shape into logs about 2 inches (5 cm) in diameter and wrap tightly.
To shape the soft dough log into a more perfect cylinder, use a paper-towel tube: Cut the tube open vertically along one side and nest the wrapped log inside, then tape or rubber-band the tube closed.
Chill in the refrigerator until firm, about 1 hour.
Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
On a sheet of waxed paper, combine 1 1/2 teaspoons salt and the sparkling sugar. Unwrap the dough logs and roll them in the mixture to coat well. Place each log on a cutting board
and cut into 1/8-inch-thick (3-mm-thick) rounds, arranging the rounds 1 inch (2.5 cm) apart on the prepared baking sheets.
Bake until lightly browned at the edges, about 16 minutes, rotating the pans halfway through so the cookies bake evenly.
Remove to wire racks to cool completely.
The cookies can be stored at room temperature in an airtight container for up to 1 week.