Preheat the oven to 180C/350F/gas mark 4
Use two 20cm/8 inch sandwich tins.
Grease and line the sandwich tins. Beat the butter and sugar until creamy. Add the vanilla essence and peanut butter and beat well. Beat in the sour cream. Sift the flour, baking powder and salt together. Add to the butter-sugar-sour cream mixture by sifting and folding in alternate batches of the flour and the milk, about a third of each at a time. Mix lightly but thoroughly. Spoon the mixture into the sandwich tins. Bake for 25 to 30 minutes. Remove from the oven and allow to stand for 2 to 3 minutes before turning out onto cake racks to cool. When cold, slice each cake in half horizontally, to make four layers. Filing and Icing: Beat the butter, peanut butter and vanilla essence until creamy. Add the evaporated milk and beat thoroughly, then gradually add the sifted icing sugar and carob, beating until a soft spreading consistency is obtained. Assembly:
Use about two-thirds of the filling and icing mixture for filling. Spread the mixture between the four cake layers, re-forming the cake, and gently pressing to adhere. Spread the remaining mixture on top of the cake, swirling or roughing it to an attractive design. Chill before cutting, especially in warm weather.
