In a medium bowl stir together flour, sugar, and baking powder. Using a pastry blender, cut in margarine until mixture resembles coarse crumbs; make a well in the center. Combine egg, milk, and vanilla; add to flour mixture all at once. Mix well. On a lightly floured surface knead dough gently for 10 to 12 strokes or until smooth. Chill one-third of the dough. Pat remaining dough onto the bottom and up the sides of a 10-inch tart pan. Arrange apples over pastry in the pan. Stir together preserves and sugar. Spread over apples. On a lightly floured surface roll chilled dough into a 10-inch circle. Cut into 1/2 inch-wide strips. Arrange strips over apples in lattice pattern. Trim strips to edges of the pan. If desired, brush lattice with additional milk and sprinkle with sugar. Bake in a 375 F oven for 45 to 50 minutes or until fruit is tender. Cover loosely with foil the last 10 to 15 minutes. Serve warm.