• 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.

The Vanilla Custard Filling:

• 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.

Assembly:

• 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.