1. Make the Crema Pasticcera:

1. In a medium saucepan, heat the milk over medium heat until it begins to steam (do not boil). If using a vanilla bean, split it lengthwise, scrape the seeds into the milk, and add the pod.
2. In a bowl, whisk the egg yolks, sugar, and cornstarch until smooth. Gradually add the hot milk to the egg mixture, whisking constantly to temper the eggs.
3. Return the mixture to the saucepan and cook over medium heat, whisking constantly, until thickened, about 3–5 minutes.
4. Remove from heat and stir in the vanilla extract (if not using a vanilla bean) and lemon zest (if desired). Transfer to a bowl, cover with plastic wrap (pressed directly onto the surface), and chill for at least 1 hour.

2. Prepare the Puff Pastry:

5. Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper.
6. Roll out the puff pastry on a lightly floured surface. Cut into 6 equal rectangles or squares.
7. Using a knife, score a smaller rectangle inside each piece, about 1/2 inch from the edge (do not cut through). Prick the inner rectangle with a fork to prevent it from puffing too much.
8. Brush the edges with the beaten egg and sprinkle with sugar (if using).

3. Bake the Pastries:

9. Transfer the puff pastry pieces to the prepared baking sheet. Bake for 12–15 minutes, or until golden and puffed. Let cool completely.

4. Assemble the Pastries:

10. Gently press down the center of each puff pastry to create a well. Spoon or pipe the chilled Crema Pasticcera into the center of each pastry.
11. Arrange fresh berries on top of the custard.

5. Garnish and Serve:

12. Dust the pastries with powdered sugar and garnish with mint leaves if desired. Serve immediately.