01 -
Preheat the oven to 350°F. Lightly grease a pie pan and set aside.
02 -
In a large saucepan, add the blackberries, sugar, and lemon juice. Bring to a simmer, stir in the corn starch, and cook until thickened. Let cool to room temperature.
03 -
In a bowl, mix flour and salt. Grate cold butter into the mixture and cut in until butter pieces are pea-sized. Add buttermilk and mix until dough just comes together. Shape into a disc, wrap in plastic wrap, and refrigerate for at least 20 minutes.
04 -
In a small bowl, whisk together flour, sugar, and brown sugar. Drizzle in melted butter and whisk until crumbly. Refrigerate until ready to use.
05 -
Roll the dough out on a floured surface to fit the pie pan. Press into the pan and shape edges to form the crust.
06 -
Spread the filling evenly into the crust. Sprinkle the streusel on top in an even layer.
07 -
Bake for 55-60 minutes, or until the crust is golden and the filling is bubbling and thick. Let cool completely before slicing and serving.