Soak apples in cold water to cover overnight; drain well, and chop coarsely.
Combine chopped apples and molasses; cook over medium heat, stirring gently, about 30 minutes or until apples are tender and moisture is absorbed. Set aside.
Cream butter in a large mixing bowl; gradually add sugar, beating until light and fluffy. Add eggs, one at a time, beating well after each addition.
Dissolve soda in buttermilk. Combine 3 1/2 cups flour with spices; mix well. Add flour mixture to creamed mixture alternately with buttermilk mixture, beginning and ending with flour mixture. Dredge raisins and citron in remaining 1/2 cup flour. Fold in to batter. Stir in prepared apples and vanilla.
Pour batter into a waxed paper - lined and greased 13- x 9- x 2 - inch baking pan. Bake at 300° for 1 hour and 15 minutes or until a wooden pick inserted in center comes out clean. Cool completely. To serve, cut into squares, and garnish each with a dollop of whipped cream, if desired.