Place apples and water in a 6-qt. stockpot; bring to a boil. Reduce heat; simmer, uncovered, 40-45 minutes or until apples are softened, stirring occasionally. Mash into a chunky sauce. Stir in brown sugar and pie spice; simmer, uncovered, 10-15 minutes longer or until liquid is absorbed and sauce is thickened. Cool completely., Preheat oven to 400°. In a large bowl, cream butter and sugar until light and fluffy. Add eggs, 1 at a time, beating well after each addition. Beat in vanilla. In another bowl, whisk flour, baking powder and baking soda; add to creamed mixture alternately with buttermilk, beating well after each addition., Divide dough into 8 portions; shape each into a disk. Cut out eight 9-in. circles of parchment. With a floured rolling pin, roll out a dough disk to fit each parchment circle. Transfer to baking sheets. Bake until golden brown, 10-12 minutes. Remove from pans to wire racks to cool completely., Place1 layer on a serving plate; spread with 2/3 cup filling. Repeat layers. Top with remaining cake layer, wrap tightly in plastic wrap; refrigerate 1-2 days or until layers soften. If desired, sprinkle cake with confectioner's sugar.