1. Lightly roll out the puff pastry sheet with a rolling pin. Prick it with a fork and cut out heart shapes using a cookie cutter. Brush with egg and sprinkle with sugar.
2. Bake in a preheated oven at 190 degrees Celsius for 15-20 minutes until golden brown on both sides. To prevent excessive puffing, place non-stick parchment paper over the pastry and weigh it down with a baking tray.
3. Once baked, remove from the oven and let them cool on a wire rack.
For the Pastry Cream:
1. Bring the milk to a boil. Whisk together the cornstarch, sugar, vanilla, and eggs. Pour this mixture into the hot milk and whisk well until fully combined.
2. Return to the heat to boil again and thicken into a cream. Remove from the heat and add the dark chocolate. Stir until the chocolate melts and the mixture is smooth. Cover with plastic wrap to prevent a skin from forming.
3. Chill in the refrigerator, then beat in a mixer until light and fluffy. Gently fold in the whipped fresh cream using a spatula.
For the Dark Chocolate Ganache:
1. Heat the fresh cream on the stove. Chop the couverture chocolate into small pieces.
2. Add the chocolate to the hot fresh cream and stir until combined. Serve warm.
3. Assemble the Mille-Feuille and drizzle with the warm ganache.
