Dice chicken breasts into ½ inch pieces. Set aside. In a large, heavy-bottomed pot on medium heat, add diced onions and butter and saute until translucent. Add garlic, ginger, chicken, and salt. Saute until chicken is cooked on the outside, about 5 minutes.
Add carrots, celery, and spices to the chicken and continue to stir over medium heat. After another 5 minutes, add heavy cream, corn starch, and water, and let simmer uncovered for 10 minutes. Once thickened, add ½ cup yogurt, set heat to low, stir and simmer for another 5 minutes. Cool mixture in the fridge until room temperature. Stir in the fridge every 15 minutes to speed up cooling process.
To make patties, generously flour a surface and roll out puff pastry sheets until they are even larger square sheets. Cut each rolled pastry sheet into 9 squares, resulting in a total of 18 squares. In a small bowl, mix egg and water until fully incorporated.
Spread a heaping spoonful of chicken filling into the center of one puff pastry square. Fold pastry over the mixture, creating a triangular shape. Use a fork to crimp and further seal down the edges of the patty. Arrange patties onto a parchment lined baking sheet and brush with more egg wash.
To bake immediately, preheat the oven to 400 degrees F and bake for 20-25 minutes, or until golden brown and fluffy. Alternatively, you can freeze the patties for up to 6 months and bake right before serving.