To make the cake, butter and line a 20cm round, deep cake tin. Using a slotted spoon, arrange the apples in the base, reserving the syrupy pan juices. Beat the remaining butter and sugar together until fluffy. Gradually beat in the eggs, then sift in the flour, baking powder and cinnamon. Fold in gently until combined, then spoon the mixture on top of the apples. Level the surface and bake for 30-35 minutes, or until springy to the touch.