1. Preheat oven to 350 degrees.

2. Place graham cracker crumbs, cocoa powder, turbinado sugar, and salt in the bowl of a food processor; pulse to combine. Add melted butter and continue pulsing until well combined. Add egg whites and continue pulsing until crumbs begin to stick together.

3. Trace an 8-inch circle on a piece of parchment paper. Place paper pencil-side down on a baking sheet. Turn crumb mixture out onto parchment and form into a flat, even 8-inch disc, using the tracing as a guide.

4. Transfer to oven and bake until firm and middle appears dry, 12 to 15 minutes. Let cool completely before using.