In a food processor, combine granulated sugar and the zest of one orange. Pulse until the mixture is moist and well-blended, releasing the fragrant citrus oils. This process takes about 30 seconds.

Add all-purpose flour, softened unsalted butter, salt, and optional orange extract to the orange sugar mixture in the food processor. Pulse until the ingredients come together into a cohesive clump, which should take around 1-2 minutes.

Turn the dough onto a clean surface and bring it together into a ball. Divide this ball into two equal portions and shape each portion into a log approximately 12 inches long. Wrap the logs in plastic wrap and refrigerate for about 2 hours.

Preheat your oven to 350°F (175°C). Once chilled, slice the logs into ½-inch thick rounds and arrange the cookies on parchment-lined baking sheets, spacing them about an inch apart. Bake for 10-12 minutes.

After baking, allow the cookies to cool on the baking sheets for about 5 minutes before transferring them to a wire rack to cool completely.

Melt the dark or semi-sweet chocolate until smooth. Dip each cookie halfway into the melted chocolate, allowing the excess to drip off, and place back onto parchment-lined sheets to set.