Preheat the oven to 325 degrees F.
Combine the coconut with the sweetened condensed milk, salt and vanilla in a medium mixing bowl.
In the bowl of a stand mixer with a whisk attachment, beat the egg whites on medium speed until foamy. Gradually add the sugar and continue to whip the whites until medium peaks form, 6 to 7 minutes.
Gently fold the egg whites into the coconut mixture. Scoop tablespoon-sized mounds onto a parchment-lined half sheet pan and bake for 20 to 25 minutes or until golden brown. Immediately transfer the parchment with the macaroons to a cooling rack. Cool completely before topping.
Fill a 4-quart pot with enough water to come 2 inches up the side, set over medium heat and bring to a simmer. Combine the chocolate chips and shortening in a small metal or glass mixing bowl and set over the simmering pot. Stir occasionally until melted, then remove from the heat.
Dip the cooled cookies in the chocolate mixture, sprinkle with the chopped macadamia nuts and place on parchment paper to set, about 30 minutes.
Alton prefers to use weight measurements for baking, to ensure the best accuracy. Please be careful if you try converting this recipe to standard measurements, especially for liquid ingredients. Two ounces of sweetened condensed milk is about 3/16th of a cup, which is less than 1/4 cup but more than 1/8 cup.
Recipe courtesy Alton Brown for 12 Days of Cookies 2008