Cook the potatoes in boiling salted water for 10 minutes. Lift out with a sieve. Add the asparagus, carrots, and squash to the pot and cook in the boiling water for 5 minutes. Drain well. Add the potatoes, mixed vegetables, onions, and parsley to the sauce and mix well.
For the pastry, mix the flour, salt, and baking powder in the bowl of a food processor fitted with a metal blade. Add the shortening and butter and mix quickly with your fingers until each piece is coated with flour. Pulse 10 times, or until the fat is the size of peas. With the motor running, add the ice water; process only enough to moisten the dough and have it just come together. Dump the dough out onto a floured board and knead quickly into a ball. Wrap the dough in plastic and allow it to rest in the refrigerator for 30 minutes.
Preheat the oven to 375 degrees F.
Divide the filling equally among 4 ovenproof bowls. Divide the dough into quarters and roll each piece into an 8-inch circle. Brush the outside edges of each bowl with the egg wash, then place the dough on top. Trim the circle to 1/2-inch larger than the top of the bowl. Crimp the dough to fold over the sides, pressing it to make it stick. Brush the dough with egg wash and make 3 slits in the top. Sprinkle with sea salt and cracked pepper. Place on a baking sheet and bake for 1 hour, or until the top is golden brown and the filling is bubbling hot.