In 2 quart saucepan, combine 1/2 cup sugar, cornstarch, cinnamon and nutmeg. Add corn syrup, apples and currants. Cok over medium heat, stirring frequently until mixture thickens. Remove from heat and cool slightly. In a large mixing bowl, combine flour and remaining 3/4 cup sugar. Using pastry blender, cut in margarine until mixture resembles coarse crumbs. Remove 1/2 cup and set aside for topping. To remaining mixture, stir in salt, baking powder and baking soda. Mix egg and buttermilk together. Add dry ingredients to egg-buttermilk mixture, stirring only until combined. Spray a 9 inch round cake pan with vegetable spray. Spread 2/3 of the batter over bottom of pan. Spread 2/3 of the apple mixture over batter. Dot with remaining batter and apple mixture, spreading evenly. Sprinkle with reserved crumb mixture. Bake at 350F for 45 minutes. Cool slightly before serving.