Don't let the time it takes to make this apple slab pie fool you. Almost all of the time is for chilling the dough. It's worth the wait because this no fuss pie feeds a crowd! It's made on a standard 18 by 13 sheet pan, so no pie plate required!
Combine flour, cinnamon, salt, and brown sugar in a large bowl.
With a pastry cutter, cut in butter and shortening until pea sized clumps form.
Add in vanilla and begin to add ice water one tablespoon at a time.
At this point you'll need to start working the dough with your hands.
Add water until a dough forms. Add too little and it willl be crumbly. Add too much and it will be sticky. Also try to not overwork the pastry. You want to see clumps of butter and shortening in the finished product.
Wrap the dough tightly in plastic wrap and refrigerate at least one hour.
One the dough is cold, roll it out between two sheets of parchment paper slightly larger than the size of your pan. It will help you roll it to the right dimensions.
Roll and crimp pie crust edges and pierce the bottom of crust with a fork to prevent bubbles.
Filling
Using an offset spatula, spread apple butter in the pie crust.
In a large bowl, combine oats, flour, brown sugar, almonds, salt and cinnamon,
Cut butter into the flour mixture until a crumb forms.
Top pie with crumb and chill for an hour. (This will prevent the crust from "melting" in the oven).
While the pie is chilling, preheat oven to 350F.
Bake pie 50-60 minutes, or until it's golden.
Notes
If desired, you can use an egg wash for a glossy crust. Whisk together one egg and a tablespoon of heavy cream and brush it on your crust with a pastry brush before you fill it.
Apple butters can vary widely in sweetness. If you have a sweet tooth, go for one with a bit of sugar in it. If you like a less sweet dessert, go for an unsweetened variety.
I tested this recipe with my homemade vanilla extract which is strong and made with just vodka and vanilla beans. If you don't have homemade, find the best, double strength extract you can find, preferably with little to no sugar or water added.