Preheat oven to 180°C/350°F.
Combine melted butter, cake mix, cinnamon and nutmeg in a bowl and mix well. Pour into a 28x18cm/11x7” lined cake tin and bake for 15 minutes or until still a little wobbly in the centre.
Meanwhile, combine sliced apples and sugar in a bowl and microwave for 3 minutes or until tender. Drain any liquid. Add sour cream and cinnamon to the apples. Pour onto base. It should push the cake mixture up the sides.
Bake for a further 15-20 minutes or until just set. Refrigerate until cold. Slice and serve with whipped cream and maple syrup.