In a heavy saucepan over low heat, melt the cocoa butter and chocolate together until smooth.
Stir in the sifted powdered erythritol, then stir in the cocoa powder, until smooth. Remove from heat and stir in vanilla extract.
Pour into chocolate molds or spread in an 8x8 pan lined with parchment paper.
Refrigerate until set, then remove from the molds or chop into small chunks.
