In a food processor, pulse the flour and salt. Add the butter; pulse to the size of peas. Sprinkle the ice water over and pulse until the pastry starts to come together. On a work surface, gently knead the pastry a few times. Shape into a disk, wrap in plastic and refrigerate until firm, 1 1/2 hours.
In a Dutch oven, heat 1 tablespoon of the oil. Season the lamb with salt and pepper and add half to the casserole. Cook over high heat until browned on 2 sides, about 3 minutes. Using a slotted spoon, transfer the lamb to a bowl; repeat with 1 more tablespoon of oil and the remaining lamb. Pour off the oil in the casserole.
Add the remaining 1 tablespoon of oil and the lamb to the casserole. Add the onion and cook over moderate heat, stirring, until softened. Add the curry powder and cook, stirring, for 1 minute. Stir in the flour, then slowly stir in the wine until smooth. Add the stock and bring to a boil, stirring, until thickened, 1 minute. Cover and simmer over low heat until the lamb is very tender, 1 hour.
Add the squash, kale, carrot and coconut milk to the casserole and simmer over moderately low heat until the vegetables are tender, 10 minutes. Season with salt and pepper. Stir in the parsley and let cool.
Preheat the oven to 375°. Spoon the curry into a buttered 8-by-11-inch baking dish. Brush the dish rim with beaten egg. On a lightly floured surface, roll out the pastry to a 14-by-12-inch rectangle. Fold the pastry in half, unfold it over the curry, and gently press onto the edge of the dish. Brush with beaten egg; cut 4 small steam vents in the top.
Bake the potpie for 40 minutes. Raise the heat to 450°; bake for 20 minutes longer, until the pastry is browned and cooked through. Let rest for 20 minutes, then serve.