4 pie crusts, store-bought or homemade, softened according to package directions
1 large egg
1 tablespoon water
Vanilla ice cream, for serving
Preheat oven to 375°F.
In a large bowl, mix together frozen berries, sugar, flour, cinnamon, salt and lemon zest.
Lightly flour a work surface. Place one pie crust on top of a second pie crust and roll out into a 12x17” rectangle. Transfer to a 10x15” rimmed baking sheet.
Pour the fruit filling into the baking sheet and spread into an even layer.
Place the remaining two pie crusts on top of each other and roll into a 12x17” rectangle.
Cut into 1 1⁄2”-thick diagonal strips. Place half the strips diagonally across the pie filling allowing for even spacing. Place the remaining strips at right angles on top to create a lattice pattern. Trim excess dough from the ends.
Fold edge of bottom crust over the strips, seal and crimp.
Whisk together egg and water and brush over the pie dough.
Bake 45-55 minutes, or until the filling is bubbly and the lattice is golden-brown.
Allow to cool slightly, and serve with vanilla ice cream.