Mix in a stand mixer, by using the paddle, the butter with the coconut icing sugar.
Add the almond powder, the barley flour and the cacao.
Finish with the egg yolk.
Flatten the dough at 2 mm and keep refrigerated.
Roll out on 2 mm and line 2 tarts of 14 cm diameter.
Bake at 140°C during 10 minutes.
Sprinkle some Mycryo cacao butter over the tarts immediately when they come out of the oven.