Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper.

In a saucepan, combine the water and unsalted butter. Heat over medium heat until the butter is fully melted and the mixture comes to a gentle boil.

Reduce the heat to low, and quickly add the almond flour, coconut flour, baking powder, and a pinch of salt. Stir vigorously until the mixture forms a smooth dough that pulls away from the sides of the saucepan.

Remove the saucepan from the heat and allow the dough to cool for a few minutes.

Beat in the eggs, one at a time, stirring well after each addition. The dough should become smooth and glossy.

Using a piping bag or a spoon, drop small mounds of dough onto the prepared baking sheet, leaving space between them.

Bake in the preheated oven for 25-30 minutes or until the choux pastry puffs are golden brown and have a hollow sound when tapped. Do not open the oven door during baking.

While the choux pastry is baking, prepare the vanilla custard filling. In a saucepan, heat the unsweetened almond milk until it’s hot but not boiling. Remove it from the heat.

In a separate bowl, whisk together the powdered erythritol, egg yolks, almond flour, and vanilla extract until smooth.

Slowly pour the hot almond milk into the egg mixture, whisking constantly.

Return the mixture to the saucepan and cook over low heat, stirring constantly, until it thickens into a custard-like consistency. Remove it from the heat and let it cool.

Once the choux pastry puffs have cooled, use a knife to make a small slit in the side of each puff.

Fill each puff with the vanilla custard filling using a piping bag or a spoon.

Dust the filled puffs with powdered erythritol for garnish.