Prepare the pie crust dough first. Cut the butter into small cubes and place it into the freezer for 10 minutes. Into a food processor, add the flour and salt. Add the chilled butter, then pulse for about 30 seconds until a crumbly mixture forms with small bits of butter. Add the cold water next and run the food processor until a dough ball forms, about 30 seconds.
Line your counter with plastic wrap and shape the pie dough into disk in the center. Wrap the dough well and place it into the refrigerator to chill for 1 hour. You can also make this dough the day before.
Making the Filling:
Next, prepare the berry filling. If using frozen berries, thaw them first. Place all the berries into a large mixing bowl and add the sugar, lemon juice, vanilla, flour, and cornstarch. Zest the large orange and add the zest to the mixing bowl. Using a spatula or spoon, gently combine everything together until the berries are well coated in flour/cornstarch.
Preparing the Berry Pie:
Being preheating the oven to 350F/177C. Divide the chilled dough, using 2/3 for the bottom crust and 1/3 for the lattice top. Lightly flour your worksurface and rolling pin, then roll out the bottom crust into a large circle, approximately 11 to 12-inches (28 to 30-cm) in diameter, a few inches larger than your pie pan. Transfer the dough into the pan, then gently press into place and pierce the bottom with a fork all over.
Fill the pie with the mixed berry mixture, very gently pressing them into the pan. Mound the berries toward the center.
Next, roll out the remaining pie dough into a 9-to-10-inch (23 to 25-cm) circle. Using a knife or fluted pastry wheel, cut thin and/or thick strips of dough for the lattice top. Make the lattice top by laying strips of dough going one way, then perpendicular the other way. Working in sections, fold half of the pieces back, then lay them alternating over each other – over, under, over, under, over. Do this until all the strips are overlapping. Watch my video to see how it’s done!
Once the lattice is in place, go around the edges and press the dough together around the edges, then trim off the excess, leaving about 1-inch overhang. Pinch the dough around the edges to create a decorative border. Watch my video to see how I made mine!
Last, apply the egg wash. Beat 1 egg with a few drops of water in a measuring cup, then using a pastry brush to coat the lattice top and the edges. Sprinkle the top with sugar sprinkles, if desired.
Baking the Pie:
Bake the pie in the preheated oven at 350F/177C for approximately 1 hour, up to 1 hour and 15 minutes, until the pie crust is golden. At the 30-minute mark, add a pie crust protector or foil shaped to fit around the edges, to prevent the crust from burning. Also, place a sheet of foil on the rack below to catch any berry juices.
Once the pie is done, very carefully remove it from the oven. It will be extremely hot! Allow it to cool on a wire rack for 3 to 4 hours, then transfer it into the refrigerator to cool further, if desired. The pie can be enjoyed warm, too.
Serve the pie a la mode with a scoop of vanilla ice cream or whipped cream with each slice.