Make the Choux Pastry:

• Preheat oven to 375°F (190°C). Line a baking sheet with parchment paper.
• In a saucepan, heat water, milk, butter, sugar, and salt until it begins to simmer.
• Add flour all at once, stirring vigorously until the dough forms a smooth ball and pulls away from the sides of the pan.
• Remove from heat and let it cool slightly for a few minutes.

Add the Eggs:

• Add eggs one at a time, mixing well after each addition until smooth and glossy.
• Transfer the dough to a piping bag and pipe small mounds onto the prepared baking sheet.

Bake the Puffs:

• Bake for 25-30 minutes until golden brown and puffed.
• Remove from the oven and let them cool completely.

Make the Vanilla Custard:

• Heat milk in a saucepan over medium heat until warm (but not boiling).
• In a separate bowl, whisk together sugar, egg yolks, and cornstarch until smooth.
• Slowly add the warm milk to the egg mixture, whisking constantly.
• Return the mixture to the saucepan and cook over low heat, stirring continuously until thickened.
• Remove from heat and stir in vanilla extract and butter. Let cool completely in the fridge.

Fill the Cream Puffs:

• Slice the cooled puffs in half and pipe the vanilla custard inside.

Garnish & Serve:

• Dust with powdered sugar or drizzle with melted chocolate for an extra indulgence.