Coarsely chop the chocolate with a sharp chef’s knife. Or use chocolate chips. Place the chocolate and butter in a shallow bowl. Microwave in two 30-second sessions, stirring after each session, until the chocolate is almost melted.
Stir in the heavy cream. Microwave for 20 more seconds, then stir the mixture with a rubber spatula until it turns into a smooth ganache, as shown in the video below. You can stir in a bit of stevia at this point if you'd like.
Cover the mixture with a plastic wrap and freeze for 30 minutes.
Now comes the fun (and messy!) part, so you might want to use disposable gloves: Scoop out small portions of the mixture, measuring about 1 tablespoon per truffle. Shape the truffles with your hands into balls. They won’t be perfectly round.
Roll the truffles in the cocoa powder to coat. They're ready! Enjoy.