Preheat your oven to 180°C or 350°F and line a baking sheet with a silicone mat or parchment paper.
Mix together the ground flaxseeds and the 75g of water and set aside to thicken.
Whisk together the flour, baking powder and salt and set aside.
In a bowl, whisk together the cocoa powder, sugars, vanilla, oil,the 55g of water and coffee until completely smooth.
Add the flaxseed mixture and stir followed by the flour mixture. Combine without overmixing.
If your dough is too soft to form balls, you can cover it and pop it in the fridge for 30 minutes.
Put the powdered sugar in a small bowl.
When the dough is ready, form it into ping pong sized balls (35g if you want to weigh them) and roll in the powdered sugar before placing them on your lined baking sheet. They spread a bit so leave some room between each ball.
Bake for 10 to 13 minutes and let them cool completely on the baking sheet before storing.