In a medium bowl, whisk together all ingredients except the cocoa powder until smooth.
Cover with plastic wrap and refrigerate for about 2 hours or until firm but still scoopable. If it's too firm, let rest at room temperature until scoopable.
Use a cookie dough scoop to scoop a dollop of the chocolate mixture out of the bowl, then roll it into a ball. Repeat with the remaining chocolate mixture, setting aside each truffle as you go.
Pour the cacao powder into a shallow bowl and roll each truffle into the powder, coating generously.
Enjoy immediately or store in an airtight container in the refrigerator.
