Hot Water Pastry
¾ cup butter, cubed
¾ cup water
2¾ cups all-purpose flour (add a bit more if too sticky) 330g
¾ teaspoon kosher salt
1 egg
1 tablespoon milk
Combine the cubed butter with 1 cup of water in a large saucepan. Bring to a boil and, once the butter has melted, remove from the heat and add the flour and salt. Stir well until everything comes together.
Turn the dough out onto a lightly floured work surface and allow to cool slightly. When cool enough to handle, knead the dough until very smooth and a little elastic.
Wrap in plastic and place in the fridge for at least 2 hours to rest and chill. The dough can be made up to 1 day in advance. You can skip placing it in the fridge, but it makes it easier to roll.
When ready to bake the pie, heat your oven to 400°F and wrap the outside of a 9-inch springform pan with aluminum foil.
Lightly dust a work surface with flour and divide the pastry into two pieces, one slightly smaller than the other. Roll the larger piece of pastry out to ¼-inch thick and transfer to the springform pan, lining the bottom and up the sides. Add your cooled filling, then roll the remaining piece of pastry to ¼-inch thick and drape over the filling, crimping the edges with a fork or by pinching with your fingers.
Beat together the egg and milk and brush over the top of the pie. Cut a vent into the center of the pastry and place on a large baking sheet in case of any bubbling over or leakage. Bake for 30 minutes, then reduce the oven to 350°F and continue to bake for 30 to 35 minutes, or until the pastry is golden brown and crisp.
Allow the pie to cool for 10 minutes before unmolding, slicing, and serving.