Preheat oven to 120°C.
Combine the chopped macadamias and ¼ cup of the castor sugar in a food processor and process until finely chopped. In a separate bowl beat the egg whites and cream of tartar until soft peaks form. Gradually beat in remaining cup of sugar until sugar has dissolved and mixture is stiff. Fold in the macadamia mixture and both gingers.
Place teaspoon of mixture on oven trays lined with baking paper, allowing room for spreading. Top each with a macadamia and bake for 40-45 minutes or until dry and crisp but not browned.
To make chocolate meringues, substitute 2 teaspoons of cocoa powder for the ginger powder.