Pulse the flour, sugar, and salt in a food processor until combined. Alternately, whisk together the flour, sugar and salt in a large bowl.
Add in the butter pieces and pulse until the mixture looks like coarse meal. If mixing the dough in a bowl, use your hands or a pastry cutter to incorporate the butter.
Sprinkle with 4 Tablespoons of water and pulse until dough comes together. Add in the last Tablespoon of water if needed for the dough to come together.
Remove the dough from the food processor and shape into a flat disk and wrap in plastic wrap. Chill in the refrigerator for 30 minutes.
In a large bowl combine the fruit, sugar, cornstarch, lemon juice, and vanilla and stir to combine.
Place the dough on a large piece of parchment paper and roll out into a 12 inch circle.
Place the fruit mixture in the center of the dough, leaving a 2-3 inch border around the edges.
Fold the sides of the dough up over the fruit, pleating as needed.
In a small bowl, whisk together the egg with the water. Brush evenly over the folded crust (you don't need to use all of the egg wash).
Bake at 400 for 35-45 minutes until the fruit is hot and bubbly, and the crust is golden brown. Serve immediately.