For the Crust
1 Cup all-purpose flour
6 Tablespoons butter, chilled
2 Tablespoons shortening, chilled
Heavy pinch kosher salt
1/4 Cup ice water
1 1/2 Cups raspberries and/or blackberries, fresh or thawed, previously frozen
1/2 Cup sugar
2 tablespoons cornstarch
You will also need:
1 Tablespoon water
First make the batch of pie crust. Add the flour, butter and shortening to the bowl of a food processor and pulse until mealy. Add 2 Tbsp. water and pulse a couple more times, adding water in increments of a teaspoon or so until the dough stays together when pinched. Dump the bowl out onto a workspace and shape into a disk, then wrap in plastic and refrigerate for at least one hour.
Next, make the filling – best to do it right after putting the pie crust in the fridge, so it has time to cool down.
Stir berries, sugar and cornstarch together in a small saucepan over medium heat. Use a potato masher or similar tool to smash the berries together and bring the mixture to a simmer. Cook at a simmer for 5 minutes, then kill the heat and allow to cool.
Preheat the oven to 425°F. When the pie crust has properly chilled, roll it out to about a 1/8 inch thickness and cut into four long rectangles, each about 4 inches by 12 inches. You will be folding these long strips in half, so make note of the approximate midline of the first pastry, then spoon about 2 Tbsp. of the berry filling into the center of one side of long rectangle. Fold the other half of the pastry closed to make a final size of about 4 inches by 6 inches. Press with your fingers to seal around the edges, then use a fork to seal it very tightly. Repeat for the other pastries.
Use a fork to mix up the egg and water, then brush the pastries liberally with the egg wash and transfer to a baking sheet. Bake for 15-20 minutes, or until the pastry is golden brown. Allow to cool before eating.
If you like, you can make a glaze. Smoosh more berries until they release about two tablespoons of juice. Strain the juice using a cocktail strainer, then use a fork to stir in 3-4 Tbsp. powdered sugar until smooth. The glaze should be thick enough to not be runny, but thin enough to drizzle. You can drizzle with a spoon, or put the glaze in a zip top bag, snip off a tiny piece of a corner and use it as a low-fi pastry bag.