Beat together butter and shortening until smooth and creamy; chill until firm. Sift together flour, sugar and salt in medium bowl.
Using fork, cut butter and shortening into dry ingredients until mixture has a consistent texture. Mix egg yolk, ice water and vinegar into dough, then form into ball and refrigerate about 1 hour.
Preheat oven to 450° F. When dough has chilled, roll it out and press into pie plate. Press parchment paper or aluminum foil into crust and weight crust down with ceramic pie weight or another pie plate filled with dried beans.
Bake 15 minutes, then remove weight or pan filled with beans and prick crust with fork to allow steam to escape. Bake another 5−10 minutes or until crust is golden brown. Let crust cool.Makes 1 8-inch pie crust Source: