Heat ghee or butter in a large stockpot over medium heat. Add onion and cook until golden and caramelized, about 20 minutes. Add jalapeno and garlic; cook 1 minute more.
Stir in ground chicken, garam masala, turmeric and 1 1/2 tsp salt. Cook until chicken is no longer pink.
Stir in diced potatoes and water; cover pot and cook, stirring occasionally, until potatoes are tender, about 25 minutes. Stir in peas and cilantro. Taste, and adjust seasoning - you'll probably need more salt.
Transfer mixture to a 2-quart (2 L) baking dish. Roll out pastry and place over top. Cut a few steam vents.
Bake at 400 degrees until crust is golden brown, about 25 minutes.