Samosa Pie

Make the filling: Heat the oil in a large skillet over medium heat. Add the onion and 1 1/2 teaspoons salt and cook, stirring occasionally, until the onion is soft and translucent, about 5 minutes. Stir in the ginger, garlic, cumin and red-pepper flakes, and cook until fragrant, a minute or two. Add the lamb and cook, stirring occasionally and breaking into small pieces, until it is just cooked through, 6 to 8 minutes. Stir in the potatoes, cover, reduce the heat to medium-low and let everything steam, stirring once halfway through, until the potatoes are just soft, about 20 minutes.

Uncover, stir in the peas and cook until just heated through, a minute or two. Stir in the cornstarch slurry, then turn off the heat and stir in the cilantro. Season to taste with salt, and let cool completely before building the pie.

When the filling has cooled, arrange an oven rack in the lowest position and heat oven to 400 degrees.

Make the pastry: Whisk the flour, salt and turmeric in a large heatproof mixing bowl. Create a small well in the center.

In a small pot, bring 2/3 cup plus 1 tablespoon/165 grams water and the shortening to a boil over medium heat. As soon as the shortening has melted completely into the boiling water, pour the mixture into the well in the flour. Use a wooden spoon to quickly stir the hot water into the flour, making sure everything gets wet. As soon as it is cool enough to handle, knead the dough with your hands in the bowl or on a clean work surface until it comes together in a smooth ball.

Wrap a third of the dough in plastic wrap and set aside. Roll the remaining dough into an 11-inch circle (about 1/8-inch thick) between two large pieces of plastic wrap or parchment paper. Remove one piece of wrap or paper and flip the pastry into an 8-inch springform pan, centering it and using your hands to gently press it into the bottom and against the sides. The dough should be supple and smooth enough that, if you tear it, you can easily patch any holes. Discard the wrap or paper. Add the filling and use the back of a spoon to press it in and level the surface. There should be a 1/2-inch rim of dough above the filling. Brush it with the beaten egg.

Roll the reserved dough into a 9-inch circle (about 1/8-inch thick) between two pieces of plastic wrap or parchment paper. Remove one piece of wrap or paper and flip the pastry over the filling, centering it and pushing it down so that it fits snugly. The edge of the top crust will overlap the edge of the bottom crust. Press these two edges together gently against the side of the pan. Using a knife, trim the top of the combined edges to create an even border around the pan, then use your fingers to crimp that bit of dough back down into the pie, sealing the edges.

Cut a hole in the center of the pie to allow air to escape, brush the top with egg and bake until the top is deep golden brown and firm, 1 hour to 1 hour 15 minutes, rotating the pan halfway through. Let cool in the pan on a rack for at least 1 1/2 hours before unmolding and serving.