Preheat oven to 450 degree F. In a bowl, stir together flour and salt. Cut in cream cheese and butter until pieces are pea-size. Using a fork, stir in ice water and vinegar until all dough is moistened. Using your fingers, gently knead the dough, just until a ball forms. Flatten dough into a disc.
Roll pastry into a 16x6-inch rectangle. Transfer pastry into an ungreased 13-3/4x4-inch tart pan with a removable bottom. (Or, roll dough into a 10-inch circle. Transfer to an ungreased 9-inch tart pan with removable bottom.) Press pastry into the fluted sides of tart pan. Trim edge. Line pastry with a double thickness of foil. Bake for 10 minutes. Remove foil; bake 8 minutes more. Cool on wire rack. Decrease oven temperature to 375 degree F.
In a heavy small saucepan combine butter, brown sugar, and corn syrup. Bring to boiling over medium heat. Remove from heat. Stir in mixed nuts and vanilla. Pour filling into cooled crust, spreading evenly. Place tart pan on a baking sheet.
Bake in the 375 degree F oven for 20 minutes. Cool on a wire rack for 15 minutes; remove sides of pan. Cool completely. Makes 10 servings.