Prepare dark chocolate and unsweetened cocoa powder.
Melt the dark chocolate using a double boiler.
Add Greek yogurt, unsweetened cocoa powder, and stevia to the melted chocolate and mix well.
Pour the mixture evenly into a container lined with parchment paper.
Chill in the refrigerator for at least 2 hours until set.
Cut the firm chocolate into bite-sized pieces and dust evenly with cocoa powder.