Preheat oven to 180°C. Generously coat a 20-cm square cake tin with non-stick cooking spray.
Mix flour, mixed spice, bicarbonate of soda and salt in a medium bowl. Combine the apple sauce, molasses and egg in a separate bowl. Using electric beaters at high speed, cream butter and brown sugar in a medium bowl until light, for about 4 minutes. Reduce speed to low and beat in the applesauce mixture.
Stir in flour mixture with a wooden spoon, just until combined. Stir in fresh ginger.
Pour the batter in the tin and smooth the surface. Bake for about 45 minutes or until a skewer inserted in the centre comes out with moist crumbs clinging to it. Cool in the pan on a wire rack for 10 minutes. Remove from pan and set right-side up on the rack. Leave to cool completely.
Scatter crystallised ginger on top of gingerbread. Mix icing sugar with a little water to make a spreadable glaze. Drizzle glaze over the crystallised ginger, letting some glaze run down the sides.
The combination of fresh and crystallised ginger gives this cake an intense flavour. When buying fresh ginger, make sure it is very firm and smooth. The skin should be glossy and a pinkish-tan colour. Fresh ginger should not look dry or shrivelled.