Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

On a lightly floured surface, roll out the thawed puff pastry until smooth and about 1/8 inch thick.

Cut the rolled pastry into equal squares, about 4 inches wide (8 total).

In a small bowl, whisk together the beaten egg and a splash of milk to create the egg wash.

Layer each puff pastry square with ham and cheese, and optionally a thin spread of Dijon mustard, seasoning with salt, pepper, and herbs as desired.

Cover each filled pastry square with another square, pressing down the edges to seal them.

Brush the tops of each pastry stack with the egg wash for a golden finish.

Place the stacks on the lined baking sheet and bake for 20-25 minutes until golden brown.

Allow to cool for a few minutes before serving warm.