1. Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
2. Roll out the puff pastry sheets on a lightly floured surface and cut each sheet into 4 equal squares.
3. Place a slice of ham and a slice of cheese on half of the squares, avoiding the edges.
4. Spread a small amount of Dijon mustard on top of the cheese, then sprinkle with dried thyme, salt, and pepper.
5. Brush the edges with beaten egg, then top with the remaining squares of puff pastry. Press down the edges to seal.
6. Brush the tops with beaten egg to give a golden finish, and use a fork to crimp the edges for a decorative touch.
7. Bake in the preheated oven for 15-20 minutes or until the pastry is puffed and golden brown.
8. Let them cool slightly before serving. Enjoy the crispy, cheesy goodness!

Remember, cooking is about feeling your way through the process. If your stacks aren’t perfectly square, that’s just part of their charm!