How to Make It
In a food processor, pulse the flour with a generous pinch of salt. Add the butter and shortening and pulse until the mixture resembles coarse meal. Add the ice water and pulse just until the dough comes together. Pat into a 6-inch log, wrap in plastic and refrigerate for at least 1 hour or overnight.
Heat 1 tablespoon of the oil in a large enameled cast-iron casserole. Season the lamb lightly with salt and pepper and add about one-quarter of it to the casserole in a single layer. Cook the lamb over moderately high heat until browned all over, about 7 minutes. Transfer to a platter and brown the remaining lamb in 3 batches, using 1 tablespoon of oil for each batch.
Add the onions, carrots, garlic, thyme and rosemary to the casserole and cook over moderately low heat, stirring occasionally, until barely softened, about 5 minutes. Return the lamb to the casserole and cook over high heat for 1 minute. Sprinkle in the flour and stir to coat the lamb and vegetables. Cook until lightly browned, about 30 seconds. Add the chicken stock, bay leaves and a pinch each of salt and pepper and bring the stew to a boil. Cover the casserole and cook over low heat until the meat is tender, about 1 1/4 hours.
Using a slotted spoon, transfer the lamb and vegetables to a platter and let cool to room temperature. Set the casserole over high heat and boil until the sauce is thickened and reduced to 4 cups, about 20 minutes. Stir in the parsley, season with more salt and pepper and let cool. Discard the bay leaves and return the meat and vegetables to the sauce.
Cut the pastry into 6 equal pieces. On a lightly floured surface, roll each piece out to a rough 7-inch round about 1/8 inch thick. Using a plate or bowl, cut out a 6-inch disk from each round. Cut 4 small vents in each disk.
Preheat the oven to 425°. Spoon the lamb stew into six 10-ounce ovenproof bowls, pie dishes or deep gratin dishes; they should be about 5 inches wide and 2 inches deep. Arrange the crusts on top. Fold any overhanging dough underneath, leaving a 1/2-inch border, and crimp the edges. Set the bowls on a large rimmed baking sheet and bake for about 25 minutes, or until the crusts are golden. Let the potpies cool for 10 minutes before serving.