1. In a large bowl, combine the chopped chicken with your spices (garam masala, turmeric, chilli powder, salt and pepper) as well as the grated garlic, ginger, and lemon juice, Greek yogurt, and 2 tablespoons of olive oil.
2. Mix well, cover and marinate in the fridge for at least 2 hours.

Preheat your oven to 390 degrees F.

1. In a deep nonstick skillet or pan over medium-low heat, melt the butter and add in the diced onions. Stirring frequently until fragrant. 
2. Add the marinated chicken mixture. Mix well, and cook until the outside of the chicken begins to brown, 3-5 minutes.
3. Add the tomato sauce, and heavy cream. Mix again, and let cook until the chicken is cooked through, and the curry has come to a simmer, approximately 5-10 minutes.
4. Add a tablespoon of olive oil to the bottom of a large oven-safe casserole or baking dish, and use a brush to make sure it coats the entire bottom of the dish.
5. Gently add the first layer of the thawed and rolled out puff pastry dough. Fill it with the cooked butter chicken curry.
6. Top with another layer of the rolled out puff pastry dough. Cut away any excess dough around the sides, and crimp the edges of the remaining dough together to seal the pie. Cut a few slits into the dough for ventilation
7. Generously brush the top of your pie dough with a the whisked egg yolk. Bake at 390 degrees F for about 25 minutes (or per your puff pastry instructions), until the pie is a beautiful and crispy golden brown. Serve, and enjoy!