Preheat the oven to 350 degrees F. Line a large baking sheet with parchment paper.
Pour the egg whites into the bowl of a stand mixer fit with a whisk attachment (or a clean medium-sized bowl if using a hand mixer.) Beat the egg whites for 4-5 minutes on medium-high speed until they reach the soft peak stage.
If using a stand mixer, transfer the egg whites to another bowl so you can keep using the stand mixer bowl. Hold the egg whites aside.
Mix together on medium speed the coconut, sweetened condensed milk, peanut butter, flour, vanilla and salt. Fold the egg whites into the coconut mixture using a rubber spatula - do this gently until the egg whites are incorporated.
Use a 2 tablespoon-sized cookie scoop to scoop the mixture onto the prepared baking sheet, spacing them evenly.
Bake the macaroons for about 19 minutes, until they are very lightly browned along the bottom edge and in a few spots on the tops. Transfer the macaroons to a cooling rack. Cool the macaroons completely.
Melt the chocolate:
Bring water to a simmer in the bottom pan of a double boiler. Place the chocolate chunks or chips plus the vegetable shortening in the top pan and place it over the simmering water.
(If you don't have a double boiler, use a medium saucepan for the water and a heatproof bowl to sit on top of the pan.)
Stir the chocolate mixture until everything has melted and the chocolate is smooth.
Dip the macaroons:
Line a baking sheet or work area with wax paper.
Dip the cooled macaroons one at a time in the chocolate, just enough to coat the bottoms and edges. Set the dipped macaroons on the wax paper-lined baking sheet.
Let the macaroons cool and set for about two hours.
The macaroons can be stored in an airtight container at room temperature for up to 5 days.
Makes about 29 macaroons.
OPTION: Temper the chocolate
Divide the chocolate chunks or chips into two groups.
Bring water just to a simmer in the bottom pan of the double boiler. Place half of the chocolate into the top pan of the double boiler (or into a bowl set over the lower pan.) Have a digital thermometer ready and stir the chocolate constantly as it melts.
When the temperature reaches 115 degrees remove the pan or bowl from the heat.
Now you want to bring the temperature down to about 95 degrees: stir the chocolate checking the temperature periodically: it took my melted chocolate about 7 minutes to cool to 95 degrees.
Place the pan or bowl with the chocolate back over the pan of simmering water, and add in the rest of the chopped chocolate. Stir it constantly to melt everything, and you'll have a pan of very smooth, thick chocolate.
The egg whites in this recipe, once whipped up and folded through the batter give the macaroons added structure and lift.
For the bottoms the easiest way to melt the chocolate is in the top of a double-boiler, or in short bursts in the microwave with a stir between every burst. A little vegetable shortening is added to the chocolate to help it set up quickly.
Another option is to temper the chocolate while melting it. This method requires you to monitor the temperature with a digital thermometer. Tempered chocolate sets up quickly, has a beautiful sheen, and has a nice snap when you bite into it. Want to try it? My directions for tempering are listed as an OPTION in the recipe. This tutorial for a microwave method from America's Test Kitchen is also very good.