Using a food processor, chop the coconut with 2 tbsp. confectioners sugar for 20 seconds. Scrape down and repeat until finely ground. Add the flour and pulse to mix.
Using an electric mixer, combine the butter, remaining 6 tbsp. confectioners sugar, the vanilla and salt; mix at low speed until just blended. Add the nut flour and mix just until incorporated.
Preheat the oven to 325 degrees . Line 1 cookie sheet with parchment.
On a floured surface, roll out the dough 1/3 inch thick. Cut 1 into 1/4-by-3-inch rectangles. Transfer to the prepared pan; refrigerate for 20 minutes.
Bake the shortbread until light golden, about 25 minutes. Using a wooden skewer, poke 4 little holes down the middle of each warm cookie. Let cool on the pan.
Place two-thirds of the chocolate in a microwavable bowl. Microwave at medium power for five to six 30-second intervals, stirring in between, until smooth. Add the remaining chocolate, then let stand for 5 minutes. Stir until smooth.
Dip both long edges of each cookie into the chocolate. Let cool until set, about 1 hour.