Cream sugar and eggs until thick and pale; sift flour and baking powder together; add flour mixture to creamed mixture in batches, beating until smooth between additions.
Pour into greased 9x13 baking dish; place apple slices on top of batter in one layer, overlapping them a bit; drizzle butter over apples.
Stir dark brown sugar and cinnamon together and distribute it evenly over the top of the apples.
Bake at 350°, 45 minutes or until cake tester comes out clean.