In a medium bowl, combine the sugar and orange zest. Use a fork to work the zest into the sugar until the sugar becomes moist and fragrant.

In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl with a hand mixer, cream together the butter and sugar until light and fluffy. Add vanilla and egg and beat until incorporated.

In a medium bowl, whisk together the flour and salt.

With the mixer on low, gently add dry ingredients into the butter mixture. Mix until ingredients are well combined and a stiff dough is formed.

Cut two large pieces of plastic wrap. Divide dough in half placing one half of the dough on each piece of plastic wrap. Use your hands to form two 1 ½-inch diameter logs. Open the plastic wrap and sprinkle logs with sanding sugar (if using) and roll a bit more to coat the logs well in the sugar. Wrap logs tightly in the plastic wrap, place on baking sheet and freeze logs for 1 hour or until firm.

Preheat oven to 375°F. Line two baking sheets with parchment paper.

Remove dough logs from the freezer and remove the plastic wrap. Slice dough into ¼ inch thick slices and place on prepared baking sheets 1 inch apart.

Bake until cookies are just golden at the edges, about 16-18 minutes. Allow cookies to cool on wire racks.

Store cookies in an airtight container for up to 4 days.