In a medium bowl, combine the cocoa, all-purpose flour, and salt. Set aside.

Using a hand or stand mixer, beat the butter and granulated sugar until combined.

Add the egg, milk, and vanilla extract and mix until combined.

Add in the cocoa mixture and beat on low until just combined.

Wrap the dough in plastic wrap and place in the freezer for 20 minutes to firm.

Roll the dough into 1-inch balls and roll each cookie dough ball in the nonpareils, tossing to coat the entire thing.