For the spice blend: Mix all the ingredients together. Store at room temperature in an airtight jar for up to 3 months.
For the chicken pot pie: Preheat the oven to 425 degrees F. Heat the oil in a large ovenproof skillet, braiser or pot over medium-high heat. Sprinkle the chicken thighs generously on both sides with salt and pepper and place skin side down in the skillet. Cook until the skin is golden and crisp, about 10 minutes. Then turn the thighs over and transfer the pan to the oven and bake until an internal temperature of 165 degrees F, 10 to 15 more. (Alternatively, you can turn the chicken thighs and on the stove and not for 15 to 18 minutes more, but it might get spitty!.) Transfer the chicken to a plate leaving the fat in the pan. Heat the pan over medium and add the onion, carrot, celery and a pinch of salt and cook, stirring, until softened, 7 to 10 minutes. Add the ginger and hawaij to the vegetable mixture and cook for another minute, add the flour and cook, stirring, for another minute.
Meanwhile, bring the stock to a simmer in a small saucepan. Gradually add a ladle of the stock into the vegetable mixture and cook, stirring, allowing it to thicken before adding another ladle full. Stir in the dill, parsley and peas and then reduce to low. Pull the chicken off the bones, discard or snack on the skin, chop the chicken into bite-size pieces and add it to the pan. Stir in the heavy cream. Taste and adjust seasoning as desired.
Ladle into 4 1/2-quart oven proof bowls or cocottes and place them on a rimmed baking sheet, which will make them easier to transfer and will also catch any of the mixture that overflows in the oven.
On a work surface, roll out the puff pastry sheet so that it's big enough to cut into 4 squares that are about an inch larger than the bowls. Cut into four equal squares and cut two slits in the center (it's easiest to do this while the puff pastry is on the counter versus on top of the pies). Lay the puff pastry on top of the bowls so that it sits comfortably. Brush the tops with egg wash and sprinkle with a pinch of flaky salt and cover liberally with sesame seeds. Bake until the pastry is golden, about 20 minutes. Let cool slightly and serve.