Preheat the oven to 180˚C (160˚C for fan assisted ovens)/ Gas Mark 4.
Mix the eggs, oil, water, treacle, cinnamon, nutmeg and cake mix gently together and whisk (by hand or electric mixer) for 2-3 minutes until smooth and creamy. Fold through the stem ginger.
Pour the cake mixture evenly into your two 2 x 8" well-greased cake tins.
Bake in the oven for 23-28 minutes, or until a rounded knife inserted into the centre of the cake comes out clean, then cool on a wire rack.
Spread 1/3 of the cream cheese icing over one of the cakes. Place the second cake on top and spread the remaining icing over the top and sides of the cake, using the tip of the palette knife to give a textured finish.
Gently press some of the ginger biscuit crumbs all around the base of the cake. Sprinkle some of the remaining crumbs into a circle in the centre of the top of the cake and use the rest to create a 3-4cm border all around the top edge.