Chocolate Wafers for the Cookie Crust

In a medium bowl, whisk together the flour, cocoa, and salt.

In the bowl of a stand mixer fitted with the flat beater, beat the brown sugar, granulated sugar, butter, and vanilla on medium speed until light, about 5 minutes, scraping down the sides of the bowl occasionally. Add the egg whites and beat until smoothly incorporated, about 30 seconds. Scrape down the sides of the bowl and a