Combine flaxseed meal and water in a small bowl to create a flax egg. Set aside for 10 min, stirring again at the midway mark to help the flax absorb the water. It should be thick, somewhat gel-like, and not watery.
Whisk all dry ingredients in a large bowl and set aside (flour, cocoa powder, baking powder, baking soda, salt).
In a medium bowl whisk together the wet ingredients with the flax egg until combined (melted butter, sugar, milk, and vanilla)
Pour the wet ingredients into the bowl of dry ingredients. Using a spatula, stir and fold until dough is combined, making sure to scrape any dry powder at the bottom of the bowl. (The dough will be very thick and a little sticky). Wrap the dough in cling wrap and place in the fridge for 2-3 hours. This will make it much easier to handle and yield evenly-shaped cookies.
Preheat the oven to 350 °F (177 °C). Line a large baking sheet with parchment paper (or two standard-sized sheets). Prep two small bowls for sugar coating - one with powdered sugar and one with cane sugar,
Scoop out 1.5 tablespoons of dough and place it on the baking sheet. Continue until all dough is scooped (A medium-sized cookie scoop works well for this). Now, using your hands, roll each piece of dough into a smooth ball then dip into the cane sugar to lightly coat all sides, then immediately dip into the powdered sugar to generously coat all sides. Place each piece back on the baking sheet about 2 inches apart. Continue until all of the pieces are coated.
Place in the oven for 10-12 minutes until they have spread, are crackled, and are slightly set around the edges. They will look undercooked, but that’s normal and they will continue to cook on the baking sheet out of the oven (don’t leave them in the oven too long). Let them sit on the baking sheet for 5-10 minutes then place them on a cooling rack for at least 10 more minutes. Enjoy!