1. Preheat the oven to 375 degrees. Line two baking sheets with parchment paper. In a small bowl, whisk together the cocoa and flour.
2. In a mixer fitted with the whisk attachment, beat the egg whites and salt at medium speed until frothy. With the mixer running, gradually add the confectioner's sugar. When all the sugar has been added, raise the speed to high and beat until the whites have a marshmallow-like consistency.
3. Beat in the vanilla.
4. Reduce the speed to medium and beat in half the melted chocolate, then half the cocoa-flour mixture, scraping the side of the bowl. Repeat with the remaining chocolate and cocoa-flour mixture.
5. Fold in the cherries and pistachios; let the mixture sit until thick enough to scoop, about 5 minutes.
6. Scoop the cookie dough onto the cookie sheets by level teaspoonfuls, leaving about an inch between cookies. Bake 6 to 8 minutes, until the cookies are brown and crackled on the outside.
7. Let the cookies cool on the baking sheets for 1 minute, then transfer them to a wire rack. The cookies can be stored in an airtight container up to 1 week.