In a large bowl, use the paddle attachment on your mixer to beat the butter for 1 minute on medium speed until smooth and creamy, scraping down the sides of the bowl as needed.
Add the coconut sugar and beat on high speed until fluffy.
Add the egg and vanilla and beat on high speed, scraping down the sides of the bowl as needed.
In a medium bowl, whisk together flour and cocoa powder. Add baking powder and salt, and whisk to combine.
Slowly add the dry ingredients to the bowl of wet ingredients and mix on low speed until combined. Dough will be very thick and dark like charcoal.
Place parchment paper on a baking sheet (or large nonstick silicon mat on your counter), and scoop dough into the middle of the prepared sheet. Place another piece of parchment on top and use a rolling pin to spread dough out to ¼" thickness. Place in fridge for at least 1 hour to chill.
Preheat oven 350°F. Line two baking sheets with silicone baking mats or parchment paper and set aside.
Remove dough from the fridge and use cookie cutters to cut out each cookie. Keep re-rolling the dough as needed until it's all used - if you find it getting too warm, place it back in the fridge before you keep cutting.
Place on prepared baking sheets with a little room between each. You don't have to leave as much room as you would with other cookies because these won't spread, but don't make it too crowded!
Bake for 9 minutes (this is the time I found ideal for larger cookies - if yours are smaller, start with 7 minutes and go from there). Allow to cool on baking sheet for a few minutes, then transfer to a wire rack to cool completely.