Preheat & Prep – Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper.
Cut the Pastry – Roll out the puff pastry sheet and cut it into 4 equal squares.
Assemble the Pockets – Spread a little Dijon mustard (if using) on each square. Place a slice of ham and a sprinkle of cheese on one side of each square.
Seal the Edges – Fold the pastry over the filling to form a triangle or rectangle. Press the edges with a fork to seal them.
Egg Wash & Bake – Mix the beaten egg with a teaspoon of water and brush over the pastry tops for a golden finish. Bake for 15–18 minutes, or until puffed and golden brown.