For the chocolate cream

1. In a bowl, add a small amount of the milk, the sugar, corn flour, vanilla extract and egg yolks. Whisk until fully dissolved and smooth.
2. Pour the remaining milk into a saucepan and bring it to a boil. Add the corn flour mixture and stir continuously until the cream thickens.
3. Add the chocolate, lower the heat and stir until fully melted. Add the butter and mix until melted and the cream becomes glossy.
4. Transfer the cream to a glass bowl and cover with plastic wrap directly touching the surface to prevent a skin from forming. Let it cool, then refrigerate until well chilled.

For the puff pastry

1. Remove the puff pastry from the freezer and place it in the refrigerator for 3–4 hours to thaw.
2. Preheat the oven to 200°C (fan). Line a baking tray with parchment paper and lightly dust with flour.
3. Remove the puff pastry from its packaging and place it upside down on the tray. It should be cold from the refrigerator so it cuts more easily.
4. Using a heart-shaped cutter, cut two large hearts (about 24 cm). Cut extra hearts for decoration.
5. Prick the pastry with a fork to prevent it from puffing too much during baking and sprinkle lightly with sugar.
6. Cover with parchment paper and place another baking tray on top to keep the pastry flat while baking.
7. Bake for 12 minutes, then remove the top tray and parchment paper and continue baking for another 6 minutes, or until golden.
8. Remove from the oven and allow to cool.
9. Bake any remaining puff pastry on a lined tray until golden, let it cool and crumble it.

For assembly

1. Lightly whisk the chocolate cream to make it smooth and velvety. Transfer it to a piping bag fitted with a star nozzle.
2. Place one puff pastry heart on a serving plate. Pipe a generous layer of chocolate cream on top and sprinkle with strawberries.
3. Cover with the second heart and repeat with more cream, strawberries and blueberries.
4. Finish with the crumbled puff pastry and decorate as desired. Dust with powdered sugar.
5. Refrigerate for at least 1 hour before serving.