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

Unfold one sheet of thawed puff pastry on a lightly floured surface and gently roll to smooth seams and enlarge to about 10 x 12 inches. Repeat with the second sheet.

Poke the pastry all over with a fork to prevent too much puffing. Trim edges for neat rectangles if desired.

Place both sheets on baking sheets, brush with egg wash, and sprinkle a light dusting of granulated sugar if you like added crunch.

Bake for 12–15 minutes, or until golden brown and crisp. Cool completely on a wire rack.

In a small saucepan, combine raspberries, sugar, and lemon juice. Cook over medium, stirring gently until raspberries break down and juices form (about 5–7 minutes).

Stir in the cornstarch slurry and simmer until thickened, about 1–2 minutes. Remove from heat and cool completely.

In a saucepan, heat the milk until just steaming (do not boil).

Whisk together egg yolks, half the sugar, and cornstarch until pale. Slowly temper the hot milk into the egg mixture, whisking constantly.

Return mixture to the saucepan and cook over medium heat, whisking, until thick and bubbling (about 1–2 minutes). Remove from heat, whisk in butter and vanilla.

Press plastic wrap onto the surface to prevent a skin from forming. Chill until fully cooled (at least 1 hour).

Once pastry sheets are cool, cut each into equal rectangles.

Place the bottom pastry layer on your serving plate. Spread a thin layer of pastry cream, then spoon and spread a layer of the raspberry filling. Add a second pastry layer, repeat cream + raspberry. Finish with the top pastry layer.

Pipe or spread a thin layer of whipped cream on top, dust with powdered sugar, and scatter fresh raspberries.

Chill for 20–30 minutes to let it set before slicing with a sharp serrated knife.