Place one of the pie crusts in the bottom of a 9-inch pie pan. Flute the edges if you'd like.
Combine marionberries, cornstarch, sugar, lemon juice, lemon zest and salt together in a bowl. Mix well.
Spoon the marionberry mixture into the bottom pie crust.
Cut the other pie crust into 12 strips. Lay 6 strips across the pie. Fold back every other strip. Lay one of the six remaining strips across the opposite way and fold back the strips to their original position. Repeat with the remaining strips.
Brush the top of the pie with an egg/milk wash.
Bake pie at 400 degrees for 60 - 80 minutes or until the filling is bubbly and the crust has browned. Remove from oven and allow to cool at least 30 minutes before slicing. Serve with vanilla ice cream if desired.
Notes
If you cannot find marionberries, blackberries are a good substitute. No need to thaw the frozen berries. Start watching the pie after 30 minutes. If the edges start to brown too much use a thin piece of tin foil to cover all of the edges. To reheat a slice of pie, place it on a microwave safe plate and microwave for 10 seconds. Nutrition facts for estimation purposes only.