1. Preheat the oven to 225°F (107°C) with 2 racks set evenly spaced in the middle positions. Line 2 cookie sheets with parchment paper. Set aside.
2. In the mixing bowl of the stand mixer fitted with the whisk attachment, beat egg whites and vanilla extract on medium-high (7–8) speed until foamy, 50–60 seconds. Add granulated sugar slowly in  a steady stream. Scrape down the bowl and continue beating until the meringue is shiny and very soft peaks form,  30–40 seconds.
3. Spoon the meringue onto the prepared cookie sheets in 1½- to 2-inch (4- to 5-centimeter) dollops.
4. Bake until firm and lightly browned, about 2 hours. Remove and let cool completely.
5. Place chocolate in a microwave-safe bowl. Microwave on high in 10- to 20-second intervals, stirring until the chocolate is melted. 
6. Dip the cookies in the melted chocolate so one half is coated and sprinkle with chopped macadamia nuts. Place the cookies on a cookie sheet. Let stand until set.

Pro Tip:
Before making the meringue, clean the mixing bowl with half a lemon; this eliminates any residual fat and adds acid for a sturdier meringue.