Preheat the oven to 180 degrees C. Grease and flour a 25cm ring tin.
In a large bowl cream together the butter and white sugar until smooth. Beat in the eggs one at a time, mixing well after each, then stir in the vanilla. Combine the flour, bicarb soda, salt and nutmeg; mix into the batter just until smooth. Stir in sour cream. Spoon batter into the prepared tin and spread evenly.
Bake for 1 hour and 20 minutes in the preheated oven. Cool for at least 10 minutes before inverting pan onto a plate and tapping out the cake. Dust with icing sugar before serving.