Preheat the oven to 375. Spray an 8 x 8 baking dish with cooking spray and line with parchment paper.
Melt the chocolate, sweetener, and butter in the microwave by microwaving at 30-second increments and stirring after each. When the chocolate is mostly melted stop heating the mixture and stir until smooth. (Alternatively. you can do this on the stovetop on very low heat).
Whisk in the cocoa, eggs, and peppermint extract. Pour into the prepared pan. Bake for 12-14 minutes until firm to the touch. Do not worry if some of the butter pools on top, it will absorb back into the bars. Cool completely.
Stir together the powdered erythritol, butter, cream, and peppermint extract until smooth. Drop spoonfuls on top of the bars. Spread gently. Some of the crumbs will mix into the icing giving it a cookies and cream look. Chill for at least 2-3 hours.
Run a knife around the edges of the pan and then lift the parchment paper to remove the bars. Place on a cutting board and cut into 16 pieces. Enjoy!