Pistachio Brownie Cookies

Ingredients 
3 cups powdered sugar

1/2 cup cocoa powder
2 teaspoon salt
1/2 cup egg whites (about 3 large eggs)
1/2 cup semisweet chocolate chips
1 teaspoon vanilla
4 tablespoons pistachio butter

Instructions 

1. Preheat oven to 375°F (190°C). Line two baking sheets with
parchment paper.
2. In a large bowl, whisk together the egg whites and powdered
sugar until the mixture is smooth, glossy, and the sugar has dissolved.
3. Add the cocoa powder, salt, and vanilla, then gently fold
together. The batter should look more like brownie batter than
cookie dough. Chef tip: For the most dramatic crackly tops, make
sure the egg whites and sugar are fully dissolved before folding in the dry
ingredients. A blender or stick blender works great for this.
4. Stir in the chocolate chips (optional, but never a bad idea).
5. Scoop about 2 tablespoons of batter per cookie, spacing them out on the baking 
sheet-they spread quite a bit.
6. Bake for 2 minutes at 375°F, then lower the temperature to 350°F and bake for 
another 8-9 minutes, until tops are shiny and crackly but centers are still soft.
7. Cool for 5 minutes on the tray, then transfer to a rack.
8. Once cooled, spoon 1 tablespoon of pistachio butter onto one cookie and 
press another on top to make a sandwich. These are ridiculously good out of
the oven, but even better the next day when the pistachio butter thickens and 
the cookie centers go full brownie mode.