Preheat oven to 180 degrees C. Grease and flour a 23cm cake tin. Sift together the flour, baking powder, ground ginger, cinnamon and salt. Set aside.
In a large bowl, cream together the butter and brown sugar until light and fluffy. Beat in the eggs one at a time, then stir in the grated ginger root and vanilla. Beat in the flour mixture alternately with the milk, mixing just until incorporated. Pour batter into prepared tin.
Bake in the preheated oven for 45 to 50 minutes, or until a toothpick or skewer inserted into the centre of the cake comes out clean. Let cool in tin for 10 minutes, then turn out onto a serving plate. Dust lightly with icing sugar before serving.