In a large saucepan, over low heat, melt cocoa butter and unsweetened chocolate.
Whisk until smooth and completely melted.
Remove from heat and sift in powdered sweetener and cocoa powder.
Stir in vanilla extract and whisk until incorporated.
Work quickly to pour chocolate in 3 chocolate chips mold.
If not using a chocolate chip mold, grease an 8x8 baking dish and pour evenly into the pan, spreading in an even layer.
Refrigerate until set - chocolate mold will take approximately 10-15 minutes, a baking dish will take 30-45 minutes.
Remove from mold and place in a mason jar for storage.
Remove from baking dish and chop into pieces, store in airtight container or mason jar.