Combine flours, cocoa, and baking soda in a large bowl, then add water + flax egg. Mix well.
Kneed batter into a dough.
Line a baking sheet with parchment paper and roll tiny balls (no larger than the size of a penny) and place on cookie sheet. Press each down to flatten.
Bake for 10 minutes (watch closely as they can burn quickly due to their size).
Let cool completely (cooling helps them “crisp up”).