Old-Fashioned Stack Cake

PreparationMake filling: In a large bowl combine apples and water and chill, covered, overnight. Transfer apples and water to a large heavy saucepan (at least 5 quarts) and add sugar, salt, and cinnamon. Bring mixture to a boil, stirring, and cook at a low simmer, stirring frequently, until softened, 30 to 40 minutes. Stir in vanilla and cool completely. In a food processor pulse apple mixture in batches until chopped coarse, transferring to a large bowl. Filling may be made 1 day ahead and chilled, covered. Make cake layers: Preheat oven to 400°F. In a small bowl stir together buttermilk, baking soda, and baking powder and set aside. Into a large bowl sift together 4 cups flour and salt. In another large bowl with an electric mixer beat shortening with sugar until light and fluffy. Beat in eggs, 1 at a time, beating well after each addition, and beat in vanilla. Add buttermilk mixture and beat until combined well. Gradually add flour mixture, beating until combined well. Add enough of remaining 2 cups flour, 1/4 cup at a time, to form a soft but not sticky dough. Turn dough out onto a lightly floured surface and divide into 6 pieces. Working on a lightly floured sheet of wax paper shape each piece into a disk and roll each disk into a 9-inch round. Arrange rounds on wax paper and gently prick dough all over with a fork. Bake layers one at a time on wax paper on a baking sheet in middle of oven until golden, 12 to 15 minutes. Cool layers completely on racks and carefully remove wax paper. Assemble cake: Spread 1 cup filling on one cake layer and top with another cake layer. Continue layering filling and cake layers in same manner, ending with a cake layer. (Reserve any remaining filling for another use.) Chill cake, covered, overnight and bring to room temperature before serving. Dust top of cake with confectioners' sugar and serve with whipped cream.