Preheat your oven to 400°F (200°C) and line baking trays with parchment paper.

Roll out thawed puff pastry on a floured surface and prick with a fork. Bake in the oven for 35-45 minutes until golden brown.

Let the pastry cool completely on a wire rack, then trim edges to fit an 8x8-inch square pan.

In a saucepan, combine sugar, cornstarch, and salt. Gradually whisk in warm milk and cook until thickened, about 5-7 minutes.

Remove from heat and stir in vanilla paste and butter until melted and smooth.

Layer half of the puff pastry in the pan, pour custard over it, top with remaining pastry, cover and refrigerate for at least 4 hours.

Remove from the refrigerator, slice into squares, and dust with powdered sugar before serving chilled.