Cut cold butter into ½-inch cubes and set aside in refrigerator to keep cold.
Combine flour and salt in large bowl.
Cut in butter pieces, using a pastry blender, until mixture resembles coarse crumbs with a few larger pea-sized pieces. Do not over mix.
Gradually sprinkle in water, stirring gently with fork or fingertips. Add only enough water to moisten and bind the dough.
Divide the dough in half and shape into 4 to 5-inch discs; wrap and refrigerate for 30 minutes before rolling.
Preheat oven to 425°F (if using Marionberry or similar filling.)
Roll the disc out in 12 to 13-inch circles on a lightly floured surface or between sheets of parchment paper.
Fit the first pastry circle into the bottom of a buttered 9-inch pie plate and trim the edge leaving a ½-inch overhang. Add filling.
Fit second pastry circle over the filling and trim the edges to ¾-inch overhang. Fold top edge under bottom edge and crimp to seal. Make steam vents in the top crust.
Bake at 425°F for 30 minutes; reduce heat to 350°F and bake for 25 to 30 minutes.
Marionberry filling: 5 cups Marion blackberries, 1 cup sugar, 1 teaspoon cinnamon, and 3 tablespoons cornstarch. Blend dry ingredients together, sprinkle over berries and stir to coat berries.
Butter should be cold and firm. For flaky piecrusts, it is important to not over mix. Over mixing presses flour covered fat pieces together and the dough cannot absorb enough water. The amount of water necessary to moisten the dough may vary because of temperature and humidity and the moisture content of the flour.