Combine flour and salt; cut in butter and shortening until crumbly. Gradually add ice water, tossing with a fork until dough holds together when pressed. Shape dough into a disk. Wrap and refrigerate 1 hour or overnight., On a floured surface, roll dough to fit a 9-in. pie plate. Trim and flute edge. Refrigerate 30 minutes. Preheat oven to 425°. Line unpricked crust with a double thickness of foil. Fill with pie weights. Bake on a lower oven rack until light golden brown, 15-20 minutes. Remove foil and weights; bake until bottom is golden brown, 3-6 minutes. Cool on a wire rack. Reduce oven setting to 325°., In a large bowl, whisk eggs, sugars, melted chocolate, milk, flour and vanilla. Gradually whisk in butter. Pour into crust. Cover edge with foil to prevent overbrowning., Bake at 325° until a knife inserted in the center comes out clean, 35-40 minutes. Remove foil. Cool on a wire rack. Refrigerate, covered, for 3 hours or until chilled.