Stir flour and salt together in a large bowl. Using a pastry blender, knives or your fingers, cut in margarine and butter until clumps are the size of small peas.

Drizzle in oil and buttermilk, stirring with a fork.

Turn dough onto work surface and gently bring dough together with your hands, kneading only once or twice until you can shape it into a ball. Dough should appear somewhat rough and streaked – this ensures it will be tender and flaky. Cut the dough ball in half and wrap each half in a disk shape in plastic wrap and place in refrigerator to chill for 30-60 minutes. If making one single-crust pie, freeze the other dough disk in a zip-lock bag for the next time you make pie.

Roll pastry on a well-floured surface with a floured rolling pin, rolling from center to outside edges in all directions. Turn pastry clockwise often to make sure it isn’t sticking to surface and use more flour if necessary. When dough circle is large enough to line bottom and sides of tart pan or pie plate, roll pastry around rolling pin and transfer it to the pan. Unroll pastry over pie plate or tart pan and ease it down the sides to make sure it is covering bottom and sides without being stretched. Using clean kitchen shears, trim overhang to about 1 inch (2.5 cm) and use scraps to patch any areas where there is too little dough coverage, pinching the dough into place. Fill pie shell and, if making a two-crust pie, roll out second pastry and lay it over top of pie and trim overhang to 1 inch (2.5 cm).

Fold edges under, and press dough edges together with your fingers all around the pie plate, building up a rim. Pinch a fluted pattern into the edges all around the rim of pie. Bake according to directions in pie recipe.