For the sauce, in a small saucepan combine apple juice, apple brandy, and the 2 tablespoons brown sugar. Bring to boiling. Reduce heat and boil gently, uncovered, about 60 minutes or until reduced to 1/2 cup. Set aside to cool.
Meanwhile, for the filling, in a large saucepan combine both varieties of apples, granulated sugar, the 1/4 cup brown sugar, the 3 tablespoons flour, and sage. Toss gently to coat apples. Cook over medium heat, stirring constantly, about 10 minutes or until apples are tender and juice given off by apples is slightly thickened. Set aside to cool while preparing pastry.
Preheat oven to 400 degrees F. In a medium bowl stir together the 2-1/4 cups flour and salt. Using a pastry blender, cut in shortening until pieces are pea-size. Sprinkle 1 tablespoon of the water over part of the flour mixture; gently toss with a fork. Push moistened dough to side of bowl. Repeat, using 1 tablespoon water at a time, until all the flour mixture is moistened. Divide in half. Form each half into a ball.
On a lightly floured surface use your hands to slightly flatten one dough ball. Roll dough from center to edges into a 12-inch square. Cut dough into four 6-inch squares. Repeat with remaining dough, forming eight squares in all.
Place 1/4 cup of cooled filling just off center on each square. Moisten edges of square with water; fold in half diagonally. Seal edges by pressing with tines of a fork. Prick top of turnovers several times with fork tines to make vent holes in pastry top. Brush tops with milk. With a spatula, transfer turnovers to a parchment-lined baking sheet. Bake for 20 to 25 minutes or until golden brown.
Just before serving, in a small bowl combine sour cream and vanilla; whisk in reduced apple sauce. Serve apple-sour cream sauce with turnovers. Makes 8 turnovers.