Preheat the oven to 180 Deg C.
Grease a 8-inch square cake pan with butter and flour.
Sift together the Coconut flour, baking powder and salt.
Check to make sure there are no lumps in the dark brown sugar or else just sift or break it using a fork.
In a separate bowl melt the butter.
Once melted add in the sifted cocoa powder.
Mix well until combined. Let the mixture cool slightly.
In a separate bowl whisk in the egg, sugar and vanilla, until light and fluffy. (1-2 mins).
Now add in the cooled or slightly warm cocoa butter mixture. If you add it too hot, the eggs will start cooking immediately.
Add in the sifted coconut flour, baking powder and salt mixture. Whisk until smooth.
Pour batter into prepared pan.
Let it rest for 10 minutes. This helps in coconut flour absorbing the liquids.
Bake the cake into a preheated oven for 25-35 minutes or until toothpick inserted into the center comes out clean.
Remove the cake onto a wire rack after 30 minutes.
Let it cool completely. Enjoy with a cup of dark coffee.