Preheat oven to 325°F (165°C)
Line baking sheet with parchment paper
Sift together flour, cocoa powder, salt, and baking soda
Whisk egg white until frothy
Mix in sugars, melted butter, water, and vanilla
Fold in dry ingredients until just combined
Fold in ¼ cup chocolate chips
Spread very thinly on baking sheet
Top with remaining chips and nuts
Bake 20-25 minutes until crisp
Cool completely before breaking into pieces