In a medium saucepan, combine the regular milk, heavy cream, and scraped vanilla bean pod. Warm these ingredients over medium heat while stirring gently until small bubbles form around the edges.

In a mixing bowl, whisk together the cornstarch and sugar. Gradually add in the hot milk and cream mixture, whisking continuously to avoid any lumps.

Place the mixture back into the saucepan over medium heat and continue to cook while stirring constantly until it thickens and starts to bubble gently.

Remove from heat and stir in the egg and egg yolk until fully incorporated. Ensure the mixture is smooth.

Transfer the thickened custard into a bowl, cover with plastic wrap pressed against the surface, and let it cool at room temperature for about 30 minutes.

Preheat your oven if desired and prepare the puff pastry. Unroll the chilled puff pastry dough onto a lightly floured surface. Cut into squares or rectangles.

On half of each pastry piece, dollop a spoonful of the cooled vanilla custard, leaving some space around the edges to seal.

Fold the other half of the dough over the filling to create a pocket. Pinch the edges to seal tightly.

Place the filled pastries on a baking sheet lined with parchment paper. Brush the tops with whisked egg yolk and sprinkle with sugar and vanilla powder.

Bake in the preheated oven until golden brown, allowing them to rest for a few minutes before serving.