For white chocolate filling:
- 1/2 cup sugar
- 2 tablespoons cornstarch or 1/4 cup all-purpose flour
- 2 cups whole milk
- 4 egg yolks, lightly beaten
- 4 ounces high-quality white chocolate, chopped
- 2 teaspoons butter
- 1/2 of a 17.3 ounce package frozen puff pastry (1 sheet), thawed
- 2 cups fresh berries, such as raspberries, blueberries, and strawberries
To make white chocolate filling:
Whisk together sugar, cornstarch, and milk in a medium heavy saucepan. Cook and stir on medium heat until bubbly. Cook and stir for 2 minutes more, until thickened. Remove saucepan from heat. Gradually stir half of the milk mixture into the beaten egg yolks to temper. Return egg yolk mixture back to saucepan. Bring to a gentle boil; reduce heat. Cook and stir for 2 minutes more.
Remove saucepan from heat; add white chocolate and butter, stirring until melted and smooth. Pour filling into a medium bowl and cover the surface with plastic wrap. Chill for at least two hours, or up to 24 hours in the fridge (refrain from stirring during chilling).
To assemble pastry:
Preheat oven to 425 degrees. On a lightly floured surface unfold the thawed puff pastry. Using a sharp knife, cut along creases; halve each strip crosswise to make a total of 6 rectangles. Transfer rectangles to an ungreased baking sheet. Bake about 10 minutes, or until golden brown. Remove from baking sheet; cool on a wire rack.
Split pastry rectangles in half horizontally. Place pastry bottoms on dessert plates. Spoon filling and berries over pastry bottoms. Top with pastry tops. If desired, cover and chill for up to 1 hour.