Pre-heat the oven at 375 degree.

Heat oil in a pan. Add turmeric powder, green chilies and onions along with the salt. Sauté until the onions are translucent. Do not brown them.

Add the potatoes along with coriander powder, red chilli powder and the garam masala.
With regular stirring, cook the potatoes until the mixture starts coming together.

Now, add the lemon juice and coriander leaves. Stir to combine.
Remove from heat and let the mixture completely cool.
In a bowl, lightly beat the egg along with 1 Tbsp of water and keep aside.

Line a baking tray with aluminum foil or parchment paper. Coat this with cooking spray. Set aside.
Unfold the thawed pastry sheet on a lightly floured surface.
If there are ridges in the pastry sheet, gently flatten them with a rolling pin.

Cut the sheet into either four 5-inch-by-5-inch or six 4-inch-by-4-inch squares.
Place about 2 Tbsp of potato mixture in the center of each square. I use an ice-cream scoop to make sure that al the patties have equal amount of filling.
Brush all the four sides with the egg and water solution.

Take the opposite sides of the square and fold to create a triangle. Seal the ends tight with your fingers. Then crimp them with a fork.
Place the filled patties on the baking tray.
Brush the tops and sides of these patties with the egg and water solution.
With a knife, create a small slit on top of each pastry. This will help the steam to escape during the baking.

Bake the patties on the medium rack of a pre-heated oven until they are golden brown in colour and cooked through.
Remove from the oven and serve hot with tomato ketchup.
Enjoy these savory patties with your loved ones!