Combine dry ingredients in a chilled large stainless steel bowl. Cut in butter with pastry blender or 2 knives and incorporate the fat thoroughly into the flour to resemble a consistency of coarse meal. Add shortening, sour cream and lemon juice, mix well and refrigerate for at least 1 hour
Grease and flour a 9-inch pie pan. Remove dough from refrigerator, divide mixture into 2 disks. Keep 1 disk in the refrigerator until ready for top crust. Roll dough out on a floured surface between waxed paper. Carefully transfer the bottom crust to the pie pan and trim the overhanging excess. Chill for 15 minutes to help set dough in the pan. Brush bottom with egg yolk to seal. Fill with your favorite fruit filling. Roll out remaining disk as you did for the bottom crust. Cover the pie with remaining dough. Seal and crimp the edge. Cut vents in the top crust.
Bake in the bottom half of a preheated 400 degree oven for 30 minutes. Cool thoroughly before cutting.
*Variation: Substitute vegetable oil for shortening for a pat in the pan crust.