Preheat the oven to 180C/350F/gas mark 4
Use a 20cm/8 inch baba tin.
Grease the baba tin. Cream the butter and sugar until light and fluffy. Whisk in the sour cream and mix well. Transfer the mixture to large bowl. Stir in half the sifted flour, the baking powder and 2 tbs. of milk, then stir in remaining flour and another 2 tbs. of milk. Blend the carob with the remaining 4 tbs. of milk. Stir until smooth with 2 tbs. of the cake mixture. Fold the carob mixture lightly through the cake mixture to give a rippled effect. Spoon into the prepared tin, smoothing the top slightly. Bake for about 40 minutes. Turn on to wire rack to cool. Dust with icing sugar before serving.
