Mace blade is the lacy dried covering of the nutmeg which it surrounds and protects.
It has a softer, more delicate and sweeter flavour than the nutmeg and can be used as a substitute for nutmeg in any dish.
You will often find the blades in mulled wine mixtures and they are a great flavouring for rice dishes (they can impart an orange colour), excellent in creamy/cheese sauces, soups & stews.
To use just crush between your fingers and add it in.