Mix your wet ingredients - eggs and coconut oil/butter plus vanilla extract, then add your dry ingredients - cocoa powder, baking powder, coconut flour, cinnamon and erythritol (or your sweetener of choice).
At the end, stir in your 50 g of chopped chocolate.
Fill into a silicone mould or into a regular cupcake mould using paper cups and bake for ca 20 minutes. Check that they're done - they should feel spongy when you press on them. Remove from the oven and cool.
For the Frosting
Melt the other half of the chocolate bar (50 g) in the microwave or in a pan. Stir in the double / heavy cream, butter and powdered sweetener and let it cool until it starts to thicken.
Spread over the cupcakes using a fork to make pretty patterns.
Make sure you use either a sugar free chocolate such as Lily's or dark chocolate with a minimum of 85% cocoa solids. I used a brand with 90% cocoa solids.