Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper. Cut thawed puff pastry into squares or circles and place on the sheet.

Bake for 15–20 minutes until puffed and golden brown. Transfer to a cooling rack and let cool completely.

Heat milk in a saucepan until just simmering. In a bowl, whisk egg yolks, sugar, and cornstarch until smooth.

Slowly pour hot milk into the egg mixture, whisking constantly to temper. Return mixture to the saucepan and cook until thickened.

Remove from heat, stir in vanilla extract, and cover with plastic wrap to prevent a skin. Chill until fully cooled.

Slice cooled pastry shells or make a small slit. Pipe custard into each shell using a piping bag or resealable bag.

Dust with powdered sugar and serve immediately, or chill for a refreshing treat.