Make the custard first: steam the egg yolk and water, and whisk them together. Then add the Coco Sugar®, cocoa powder, butter, and all purpose flour, and keep whisking until the custard is thickened. Lastly, add the vanilla extract, then transfer the custard into the pipping bag. Set aside to chill.
Preheat the oven at 375°F (or about 190°C).
Melt together water and butter for the cream puff pastry
Add salt and Coco Sugar® to it. Bring them to boil.
Once it starts bubbling, add the flour and stir until it gets thickened and it does not stick to the pan. Set aside to cool down.
Start adding eggs, once at the time. You might find the dough hard to be mixed with the the eggs at first, but keep stirring and you’ll get them all mixed.
Once the dough reaches a stiff peak, transfer the dough into a pipping bag.
Shape the dough on a pan, then bake at 375°F (190°C) for about 30 minutes. Do not open the oven for it will make the pate a choux shrink.
When the pate a choux is done baking, make a tiny hole in its bottom, then fill with the chocolate custard.
