Turn the oven up to 350ºF. Spread the coconut flakes onto a baking sheet lined with parchment paper. Bake the coconut for about 10 minutes until it's toasted, stirring frequently to ensure even browning and so that it does not burn. (See Kelly's Notes.) Remove the toasted coconut from the oven and set it aside.
Melt the caramels, milk and salt in a double-boiler by placing the ingredients in a medium saucepot set over a large saucepot of simmering water. Cook, stirring, until the caramels are fully melted. Remove the saucepot from the heat and combine the caramel mixture with the toasted coconut in a large bowl. Immediately spread the coconut mixture over the cooled shortbread, pressing it to adhere to the shortbread base. Work quickly, as the caramel mixture will begin to firm up and won't adhere if it cools too much. Let the bars sit at room temperature for 30 minutes.
Using the parchment paper overhangs, lift the shortbread out of the pan and onto a cutting board. Slice the shortbread into bars by spacing your cuts to make 3 columns down and 10 rows across to form 30 roughly 2-inch by 1-inch cookie bars.
Melt the dark chocolate in a double-boiler or in the microwave. Dip the bottoms of each of the cookie bars into the chocolate and place them on a wax paper-lined baking sheet. Use a fork to drizzle the tops with chocolate. Let the cookies sit until the chocolate hardens fully.