In a small saucepan, heat the heavy cream over low heat until just simmering. Remove from heat and add the chopped dark and milk chocolate. Stir until smooth and fully melted.

Let the chocolate mixture cool slightly before using.

Preheat the oven to 200°C (400°F). Line a baking sheet with parchment paper.

Roll out the puff pastry sheet on a lightly floured surface to smooth out any creases.

Cut the pastry into 4 equal squares.

Place a tablespoon of the chocolate filling in the center of each pastry square.

Fold the pastry over to form a triangle and press the edges to seal. Use a fork to crimp the edges for a decorative touch.

Brush the tops of the pastries with the egg wash mixture.

Bake in the preheated oven for 15 minutes or until golden brown and puffed.

Remove from the oven and let cool slightly before serving.