Preheat oven to 350°F / 177°C.
Line sheet pans with parchment paper or a Silpat baking mat or spray them with nonstick cooking spray.
In a medium mixing bowl, whisk together flour, cocoa powder, baking soda, and salt. Set aside.
Using a standing mixer or hand mixer, beat butter until smooth. Add both sugars and continue to mix until light and fluffy, about 3 minutes.
Add vanilla extract and eggs and mix on low until eggs are fully incorporated, stopping to scrape down the bowl as needed.
Add dry ingredients to mixer and mix on low just until everything is combined.
Pour powdered sugar into a shallow baking dish or bowl.
Roll cookie dough into 1.5-inch balls (keep these small so the finished cookies are bite-sized) and then roll the balls in powdered sugar to fully coat. (You can do this in batches, dropping a bunch of the balls in powdered sugar and then rolling them all at once.)
Place cookie dough on prepared sheet pans, leaving a couple of inches of space between them.
Bake until cookies are just barely set in the middle, 9-10 minutes.
Allow cookies to cool on sheet pan for a few minutes before transferring to a cooling rack to finish cooling.
Store in an airtight container at room temperature for up to 1 week.