1. Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper to keep things mess-free.
2. On a lightly floured surface, unfold the thawed puff pastry sheet. If it’s a bit sticky, sprinkle some flour underneath and on top to make handling easier.
3. Cut the puff pastry into four equal squares. These will be your stack bases.
4. Spread a thin layer of Dijon mustard on each square. This step is optional but adds a lovely depth of flavor.
5. Layer the ham slices evenly over each square, then sprinkle the shredded cheese over the ham. I like to add a little freshly ground black pepper here.
6. Place one puff pastry square on top of each filled square, gently pressing the edges together to seal. You can use a fork to crimp the edges for a cute, rustic look.
7. In a small bowl, whisk together the egg and water to make an egg wash. Brush this over the top of each stack to encourage a golden, glossy finish.
8. Transfer the stacks to the prepared baking sheet and bake for 15-18 minutes, or until golden brown and puffed up. Keep an eye on them—the smell of that buttery pastry baking is irresistible!
9. Remove from oven and let cool for 5 minutes before serving. This helps the cheese set a bit so it doesn’t spill everywhere when you bite in.

When I make these, I often double the recipe because they disappear fast in my house. The kids love to help brush on the egg wash, which makes the whole process feel like a little kitchen party instead of a solo task.