Preheat your oven to 400°F. Place the puff pastry sheets on a baking tray lined with parchment paper. Bake for 12–15 minutes or until golden and crisp. Let them cool completely.

In a saucepan, heat the milk over medium heat until warm but not boiling. In a separate bowl, whisk egg yolks, sugar, and cornstarch until smooth. Slowly pour the warm milk into the egg mixture while whisking constantly.

Pour the mixture back into the saucepan and cook on medium-low heat, stirring continuously until it thickens. This usually takes about 5–7 minutes. Once thick and creamy, remove from heat and stir in butter and vanilla extract.

In a chilled bowl, beat the heavy cream until soft peaks form. Gently fold the whipped cream into the cooled custard for a lighter texture.

Place one baked puff pastry sheet into the bottom of your baking dish. Spread the custard mixture evenly over it. Top with the second pastry sheet.

Refrigerate for at least 3–4 hours to set completely. Dust the top with powdered sugar before slicing into neat squares.