1. Beat the butter and Natvia until light and creamy. Add the flax egg and beat until incorporated. Sift in the cacao, flour and baking powder and add the salt. Stir with a spatula until combined.
2. Turn the dough out onto the bench and lightly knead until it is smooth. Roll out in between 2 pieces of baking paper until it is about 2cm thick. Freeze for 20 minutes. Remove and slice into 16 small rectangles.
3. Bake in the oven for 18-20 minutes. Remove from the oven and carefully place on a wire rack to cool completely.
4. Beat the coconut cream, Natvia and vanilla until combined. Whisk in the xanthum gum and chill for 20 minutes.
5. Sandwich ½ tbs of the filling in between 2 of the cookies.