24tablespoonscold butter(use the real stuff - it's far superior to margarine here)
1 ½cupsice water
6cupsfruit(mixed berries; I also used 4 ½ cups slices peaches and 1 ½ cups blueberries)
¾cupsugar
¼cupcornstarch(a heaping ¼ cup for peaches)
juice of half a lemon
a pinch of salt
2tablespoonsmilk(to brush on the crust)
sugar(to sprinkle on the crust before baking)
Instructions
Toss together flour, sugar, and salt in a very large bowl. Cut sticks of butter into ½-inch pieces. Using a pastry cutter, cut the butter into the flour mixture until the butter is the size of small peas.
Drizzle ¾ cup of the ice water into the flour mixture slowly, being careful not to deposit any ice cubes in the bowl. Use a rubber spatula to fold the mixture to distribute the water. Drizzle in additional water, 1 tablespoon at a time, until the dough begins to come together in large clumps. Use your clean hands to gently knead the clumps of dough into one mass.
Divide the dough into two uneven balls of dough; you need a slightly larger piece for the bottom crust, and a slightly larger piece for the top crust. Place each piece on plastic wrap and shape into a rough rectangle, then seal tightly. Refrigerate dough for 1-2 hours before rolling out.
When you're ready to make the pie, preheat the oven to 375F. Combine fruit, sugar, cornstarch, lemon, and the pinch of salt in a bowl. Mix well, and set aside.
Line your sheet pan with parchment paper, letting it hang over the sides; this will protect your pan from blueberry stains, and will allow you to remove the pie from the pan for cutting. Remove the larger piece of dough from the fridge. On a well-floured surface, roll it out into a 18x12 inch rectangle, or a size 2-3 inches larger than your sheet pan. Use plenty of flour to keep the dough from sticking. Try to keep your dough cold as much as possible. Gently fold your dough into quarters (I usually put a piece of plastic wrap between the layers to keep them separate), and carefully transfer to the dough to the sheet pan. The dough will hang over the sides.
Pour the prepared fruit mixture into the sheet pan and spread evenly. Try to get the sugary goo even as well. Place pan in the fridge.
Remove the smaller piece of dough from the fridge and roll out on a well-floured surface to a size 1-inch larger than your sheet pan. Remove the sheet pan from the fridge and top with the dough. Line up the dough evenly on the sheet pan. Fold the edges of the bottom dough over the top dough and pinch to seal. Use a fork to prick the top crust all over. Brush with milk and sprinkle with sugar.
Bake until crust is brown and filling is bubbly, 40-55 minutes (mine baked for 40). Cool on a wire rack for about an hour to let the filling set. I used a pizza cutter to cut mine. Serve warm or at room temperature; both are delicious.