Preheat the oven to 180 C / Gas 4. Grease two sandwich tins and dust with flour.
Cream together the butter and sugar till light and fluffy. Add the egg and stir well. Add the flour and baking powder gradually, alternating between adding the milk in batches. Finally, stir in the ginger. Pour into prepared tins.
Bake for 30 minutes, or till a skewer inserted in the centre comes out clean. Remove from oven and let cool in tins.
For the icing, cream together the icing sugar and butter. Add Nutella® and beat well.
When cake is cooled, spread icing over top of one cake, then sandwich with the other and add more icing to the top and sides.