Preheat your oven to 200°C (390°F) and line a baking sheet with parchment paper.
In a saucepan, combine the water and unsalted butter. Bring to a gentle boil until the butter is completely melted.
Remove the saucepan from the heat and quickly stir in the flour until a smooth dough forms. Return the saucepan to low heat and continue stirring for about 1-2 minutes to cook the dough slightly.
Transfer the dough to a mixing bowl and let it cool for a few minutes.
Beat in the eggs, one at a time, mixing well after each addition. The dough should become smooth and glossy.
Using a piping bag fitted with a round tip, pipe small mounds of the dough onto the prepared baking sheet, leaving some space between them.
Bake the pastry puffs in the preheated oven for 25-30 minutes or until they are golden brown and puffed up. Do not open the oven during the first 20 minutes of baking to prevent them from deflating.
While the pastry puffs are baking, prepare the custard filling. In a saucepan, heat the whole milk until it's steaming but not boiling.
In a separate bowl, whisk together the granulated sugar, egg yolks, and cornstarch until well combined.
Slowly pour the hot milk into the egg yolk mixture, whisking continuously to avoid curdling.
Pour the mixture back into the saucepan and cook over medium heat, stirring constantly, until the custard thickens and coats the back of a spoon.
Remove the custard from the heat and stir in the vanilla extract. Let it cool to room temperature.
In a separate bowl, whip the heavy cream until stiff peaks form.
Once the custard has cooled, gently fold in the whipped cream until well combined. This will create a creamy and light custard filling.
Once the pastry puffs are done baking, remove them from the oven and let them cool completely on a wire rack.
Once the puffs have cooled, use a sharp knife to cut them in half horizontally.
Fill the bottom halves of the puffs with the cream custard filling using a spoon or piping bag.
Place the top halves back on the filled puffs to create the custard cream puffs. Dust with Tate & Lyle icing sugar to finish.
Serve the cream custard puffs immediately or refrigerate them for a short time before serving. Enjoy!
Cream custard puffs are best served fresh to maintain their crispness. If you plan to make them ahead of time, store the unfilled pastry puffs in an airtight container and fill them with the custard just before serving.