Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper.
In a large mixing bowl, combine the butter, powdered coconut sugar, salt, and vanilla extract. Stir until combined.
Add the 1 cup of tapioca flour and 1/2 cup of cassava flour. Stir until combined. Stir in 1 tablespoon of coconut flour. The dough should workable with your hands now. Gently fold in the last tablespoon of coconut flour.
Pinch off tablespoon size pieces of the dough and roll them into balls. You can place the balls fairly close together on the baking sheet (but not touching) since they will not spread out.
Bake for 16-18 minutes. The bottoms of the cookies should be browned. Remove from the oven and allow them to cool for 1 minute or until you can handle them.
On a small plate, use a fork to combine the 1/4 of powdered coconut sugar and 1/4 cup of tapioca flour. Once the cookies are just cool enough to handle, gently roll them in the sugar mixture. NOTE: The cookies are VERY fragile at this point so be very gentle when rolling them in the mixture.
Optional: Roll the cookies in the mixture a second time after they have cooled for longer.