Step 1:
Start by preheating your oven to 400°F (200°C). Line a baking sheet with parchment paper to prevent sticking.

Step 2:
If your puff pastry sheets are frozen, allow them to thaw at room temperature for about 15-20 minutes or according to package instructions. While waiting, you can prepare the filling by shredding the cooked chicken.

Step 3:
In a bowl, mix the shredded or cubed chicken with salt, pepper, and garlic powder for added flavor. You can melt the butter and mix it into the chicken for extra richness.

Step 4:
Unroll the puff pastry sheets and cut each into 4 equal squares. You should have 8 squares in total. Place a spoonful of the chicken mixture onto the center of each square. Then, add a generous amount of shredded cheddar cheese on top of the chicken.

Step 5:
Fold each square diagonally to form a triangle, or fold them over as a rectangle, depending on your preference. Press down the edges with a fork to seal the pastry tightly and ensure the filling doesn’t spill out during baking.

Step 6:
Brush the top of each pastry with the beaten egg to give them a shiny, golden finish when baked. Place the pastries onto the prepared baking sheet.

Step 7:
Bake in the preheated oven for 15-20 minutes or until the puff pastry turns golden brown and crispy.

Step 8:
Remove from the oven and allow them to cool slightly before serving. The cheese inside will be hot, so give them a minute to set!