For the cupcakes:

1. Preheat the oven to 350°F. Lightly grease all 12 wells of a muffin tin. Alternately, you can use cupcake liners, or silicone cupcake molds.
2. Add all ingredients to a high powered blender and pulse until all ingredients are well incorporated and the batter is light and fluffy.
3. Fill all 12 wells of the muffin tin 3/4 of the way full.
4. Bake for 20 minutes or until you can insert and remove a toothpick without any crumbs sticking to it. Be careful not to over bake, as they will continue to cook once they are removed from the oven.
5. Allow to cool on a cooling rack while you make the chocolate buttercream frosting.

For the chocolate buttercream frosting:

1. Set up a double boiler - Heat a saucepan with 1 to 2 inches of water in it over medium heat until the water is simmering. Lower the heat to medium low. Place a glass bowl over top of the saucepan, making sure that the water is not touching the bottom of the bowl.
2. Add the chocolate chunks to the bowl and heat until melted. Remove from the heat and set aside
3. In a separate bowl, using an electric mixer, cream together the butter, erythritol, cocoa powder and vanilla extract.
4. Fold the melted dark chocolate into the butter mixture until well combined.
5. If it is too stiff, add some heavy creamy until you reach the right consistency. If is it too runny, place it in the fridge for 10 minutes before piping. But be careful to not let it fully set.
6. Pipe the frosting onto the cupcakes and enjoy!