Prepare the Dough: Cream together cold salted butter, granulated sugar, light brown sugar, and vanilla extract in a large mixing bowl until light and fluffy (about 3-4 minutes). Gradually add in all-purpose flour and unsweetened shredded coconut, mixing until just combined.

Form Logs: Divide the dough into two equal halves. Sprinkle cinnamon over each half and fold to incorporate evenly. Roll each into logs, roughly 2 inches in diameter, and wrap tightly in plastic wrap. Chill in the refrigerator for at least 1½ hours.

Preheat & Prepare Pan: Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper. Once logs are firm, remove from the fridge and unwrap.

Coat & Slice: Brush logs lightly with beaten egg, then roll in unsweetened shredded coconut. Slice logs into ¼-inch rounds and dip the sugar-side in sanding sugar for a crisp exterior.

Bake: Arrange cookies on prepared baking sheets, spacing them 2 inches apart. Bake for 10-12 minutes, or until edges are just golden brown.

Cool & Serve: Let cookies cool on baking sheets for 5 minutes before transferring to a wire rack to cool completely.