Step 1: Make the Diplomat Cream

1. In a bowl, whisk together egg yolks and sugar until light yellow. Add corn starch and mix until smooth.
2. In a saucepan, heat milk and vanilla over medium-low heat until steaming.
3. Gradually pour the warm milk into the egg mixture, whisking continuously.
4. In a separate bowl, sprinkle gelatin over cold water and let it bloom.
5. Strain the egg mixture back into the saucepan and whisk for 5-7 minutes until thickened. Remove from heat.
6. Add bloomed gelatin and butter, whisking vigorously until smooth.
7. Gently fold in whipped egg whites until fully combined.
8. Cover with plastic wrap (directly on the surface) and chill for a few hours until thick.
9. Once chilled, whip heavy whipping cream and fold into the custard until smooth and fluffy.

Step 2: Bake the Puff Pastry

10. Preheat oven to 425°F (220°C).
11. Roll out puff pastry sheets into a rectangle.
12. Place on a parchment-lined baking tray and bake for 17-20 minutes until golden brown.
13. Lightly press down the pastry with a spatula to flatten. Set aside to cool.
14. Break off small crispy pieces and save them for garnish.

Step 3: Assemble the Cake

15. Cut each puff pastry sheet into two equal rectangles (for a total of 4 layers).
16. Begin layering: place one pastry layer, spread diplomat cream, and repeat.
17. Cover the entire cake with remaining cream.
18. Press crushed puff pastry pieces onto the sides and top.

Step 4: Refrigerate & Serve

19. Cover with plastic wrap and chill for at least 4-5 hours (overnight is best).
20. Before serving, dust with powdered sugar and garnish with fresh raspberries.