Take out pastry dough and defrost according to package instructions
Boil your chicken uncovered in a small pot, using enough water so the chicken is just submerged. Add in half your salt and pepper to the water.
Once the water has reduced to a thick gravy, take the chicken out and put on a cutting board. Once cool, cut into small cubes.
Chop your onions
Heat your oil in a large pan
Add in your onions and sauté until soft & translucent, do not brown
Add in the remaining salt, pepper, and the flour. Saute for a bit then add in your chopped chicken and water/chicken stock, mixing immediately before it starts to thicken.
Simmer on low heat while stirring occasionally. Once your liquids have turned into a thick gravy/paste, take your chicken off the heat. Taste and adjust seasoning, then leave it to cool.
Preheat your oven to 400F
Separate your puff pastry, roll on a floured surface to stretch out a bit more, then cut each sheet into 4.
Divide the filling into 8 parts and spoon onto the sheets, using your spoon to spread and even it out onto half of each sheet.
Wet all the edges of your pastry sheets. Fold the empty half of the pastry sheet over the chicken filling like a blanket. Press all the edges close with your fingers. then use a fork to press onto the edges again to close them.
Use your fork to poke three holes on top of the pastry
Crack an egg in a small bowl and whisk. Brust egg onto the top of the patties, making sure to get the sides too for good coloring throughout.
Transfer your patties to a baking sheet lined with parchment paper.
Bake in the oven for 15-20 mins until deep golden brown
Let rest 5-10 minutes and serve warm, enjoy!