Spread one pie crust into the bottom of a 9” pie pan. Crimp the edges.
Preheat oven to 375℉.
In a saucepan over medium heat, add berries, sugar, cornstarch, and lemon juice and stir. Cook for 5-7 minutes until it starts to thicken, stirring occasionally and as gently as possible so you don’t break up the berries. Remove from heat and stir in vanilla and salt, then let it cool for about 15 minutes so it starts to set up.
Pour the berry mixture into the bottom crust.
Cut the second pie crust into strips, adding them in a lattice shape on top of the berries. Make sure you trim any edges that are too long, and crimp the ends of the lattice pieces to the bottom pie crust so they stay together.
Brush the top of the pie with the beaten egg, then sprinkle sugar on top of the crust.
Set the pie on a cookie sheet and bake for 45-55 minutes, until the crust is golden brown (checking at 45 minutes to see if it’s done).
Let the pie cool for several hours before serving to let it set up.
Notes
You can bake this entire pie the day before serving. Store it in the refrigerator once it has completely cooled. (Don’t cover it unless it has cooled completely or it can make the crust soggy!).