Preheat the oven to 180C/350F/gas mark 4
Use a 20cm/8 inch ring tin.
Grease the ring tin. Cream the butter, cream cheese and sugar until light and fluffy. Beat in the sour cream and mix well. Stir in the walnuts, then half the sifted flour with the carob, the baking powder and half the milk. Stir in the remaining flour and milk. Spread into the prepared tin. Bake for about 40 minutes. Test with a warm knife. Allow to stand for 10 minutes before turning out on a wire rack. Dust with sifted icing sugar before serving.
