Coarsely chop the chocolate with a sharp chef’s knife or use chocolate chips. Place the chocolate and butter in a shallow microwave-safe bowl. Microwave it in two 30-second sessions, stirring after each session, until the chocolate is almost completely melted.
Stir in the heavy cream. Microwave the mixture for 20 more seconds, then stir it with a rubber spatula until it turns into a smooth ganache. You can stir in stevia or a powdered sweetener at this point.
Cover the mixture with a plastic wrap and freeze it for 30 minutes.
Now comes the fun (and messy!) part. 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.
The truffles are ready! Enjoy.
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Notes
The only somewhat challenging part when making these truffles is shaping them. This is quite messy, so I highly recommend wearing food-safe disposable gloves when performing this task. It's not difficult to wash your hands and get rid of the chocolate, but it does tend to get under your nails.
Unless your kitchen is very warm, these truffles should last for up to three days in an airtight container on the counter. For longer storage and up to a week, it's best to refrigerate them in an airtight container. I don't recommend freezing them.
Remember to take them out of the fridge 30 minutes before enjoying them. Chocolate is always better at room temperature.