Recipe adapted from "Blackberry Slab Pie to Feed a Crowd" from Baking-sense.com.
Prepare the pie dough the day before and let it rest in the refrigerator overnight or at least 3-4 hours.
A 1/2 sheet slab pie requires a triple batch of pie dough to make You can prepare a large batch, or make three separate batches.
You can use pastry flour in place of the all-purpose and cake/flour combination.