For the Crust:
For the Pie:
Whipped cream or ice cream for serving
First things first, make the crust. Preheat the oven to 350 degrees Fahrenheit. In a large bowl or food processor mix together the graham cracker crumbs, brown sugar, flour and salt. Add the melted butter and mix until well combined and crumbs hold together. If they don't stick so well, add a bit of cold water.
Press the crumbs into a 9-inch pie plate, evenly covering the bottom and extending the crust up the sides. Freeze the crust for 10 minutes.
Meanwhile, get started on the filling. In a medium bowl, combine 3 cups of the blackberries with the granulated sugar and cornstarch. Mash the mixture with a fork to create some juice (watch out for splattering blackberry juice that will stain your clothes...we learned the hard way). Let the berries sit for 15 minutes or so.
Then, when the crust is cold, place the pie plate on a baking sheet and bake until the crust is fragrant and set, or about 15-18 minutes. Transfer the pie crust to a wire rack and allow to cool while you finish the filling.
Transfer the mashed berries to a saucepan and stir over medium heat until thickened, about 8-10 minutes, scraping the bottom of the pan to prevent too much sticking. Remove from heat and stir in vanilla extract. Taste the blackberries and if they are too tart for your liking at this point you can add some more granulated sugar.
Spoon the blackberries into the cooked and cooled crust and top with the remaining 1 1/2 cups of fresh blackberries. Serves with whipped cream or ice cream.