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

Roll out thawed puff pastry on a lightly floured surface until smooth and larger, then slice into 8 equal squares.

In a small bowl, whisk together the egg and milk to create an egg wash.

Layer fillings on each pastry square: start with ham, then cheese, and optional mustard.

Season the layers with salt and pepper, and add herbs if desired. Top with another pastry square and seal edges.

Crimp the edges with a fork for a decorative finish and tighter seal.

Brush the tops with the egg wash for a golden finish.

Arrange assembled stacks on the baking sheet, spaced apart.

Bake for 20-25 minutes until puffed and golden brown.

Cool slightly on the baking sheet before serving warm.