Preheat oven to 350ºF. Line 2 large baking sheets with parchment paper; set aside.

Combine flaxseed meal with water and let sit until gel consistency, about 5 minutes.

In a medium bowl whisk together flour, cocoa powder, baking soda and salt; set aside.

In a large bowl using electric mixer, cream together cashew butter, vegan butter and sugar until light and creamy, about 1 minute. Add in flaxseed egg and vanilla, mixing on low speed until combined.

Add in bowl of dry ingredients, mixing on low until combined. Fold in chocolate chips. Dough should be somewhat moist and thick, but not too sticky. You should be able to form a ball with your hands. 

Using medium cookie scoop (about 1.5 tablespoons) scoop dough into round shape. Roll cookie dough between hands until shaped, then place on baking sheet about 2" apart. Add chocolate chunks to top of cookie dough if desired. Gently flatten cookie with palm of hand so it's about 3/4" thick.

Bake cookies for 8-11 minutes, until edges are crisp but middles are soft – be careful not to over-bake as the cookies will set upon cooling. Let cookies rest on baking sheet for 2 minutes before transferring to wire rack.