Use only softened butter to grease the pan. Cooking spray with pool the booth of the pan created too much oil which will burn the top of the cake.
Dust with cocoa powder so your cake does not come out with white flour all over it.
Place your cake pan on a baking sheet while baking. This keeps the delicate tops from over baking and it is much easier to remove from the oven.
To Freeze: Let cake cool completely, wrap in a double layer of plastic then in foil. Freeze up to 3 months.
Use a microprobe to grate your whole nutmeg. Microplanes are available on my website from Amazon or in most kitchen shops and even some grocery stores. The pre-ground nutmeg is just brown dust. I do not recommend.