In a food processor, combine the sugar and orange zest. Pulse until combined and the zest is finely ground.

To the orange sugar, add the flour, butter, salt, and extract. Pulse to combine, then run the machine until the dough comes together into a ragged clump.

Turn the dough out and bring together with your hands. Divide in half and form 2 logs of dough, about 12 inches long each. Wrap in plastic and refrigerate until firm, about 2 hours.

Preheat oven to 350°F. Line baking sheets with parchment paper.

Slice the logs of dough into 1/2 inch slices and place them 2 inches apart on the cookie sheets.

Bake the cookies for 10-12 minutes, until just turning golden on the edges but still pale on top.

Let the cookies cool completely on a rack.

Melt the chocolate in a double boiler or in the microwave, starting with one minute, then in 15 second bursts, stirring well in between.

Dip each cookie half-way into the chocolate and set on parchment paper to harden. Sprinkle with more orange zest, if desired.