Mace and nutmeg are the fraternal twins of the spice world. Superficially, they taste pretty close, after all they come from the same seed; but mace is the younger brother that needed to be pushier to get noticed and never quite lost his edge.
Mace and nutmeg do come from the same seed. Mace is a thin reddish layer that covers the round, dense nutmeg. This skin is removed, dried and powdered. We buy it as red or yellow and it has a flavour somewhere between cinnamon and nutmeg with a bitterness that stays in the mouth.
These spices are the fragrant fruit of an evergreen tree that originated in Indonesia. They have a slight turpentiney coniferous zest that quickly moves from resin to perfume.
While common now, at one time nutmeg and mace were among the prizes of a spice highway that stretched from the far east to England. During Europe's the middle ages a pound of mace was worth as much as half a cow. In Elizabethan times, mace ale was a common drink and a mix of pepper, salt and powdered mace was advised to give piquancy to overcooked meats and vegetables.
Although they can be used interchangeably, mace and nutmeg aren't identical. Gram for gram, powdered mace is more volatile than nutmeg. Nutmeg may have a sweeter, deeper tasteit's great grated over whipped cream and custardsbut this flavour is subsumed into a dish as it cooks. Mace, however, gets left on its own. It's what you want when being subtle isn't important.
Mace works best in cooking where there are other strong flavours to compliment its own. Try mace in marinades and cheese souffles. It's the classic spice in pound cake. Use nutmeg when all you want is a whisper but go for mace when you want to carry its flavour over the top.