Beat butter and sugar together until light and fluffy.
Gradually beat in the milk and vinegar. Fold in all the flour except 1 tbsp.
Divide batter in half. Fold 1 tbsp flour in 1 half and the cocoa in the other.
Place in alternate spoonfuls in a greased and lined 8" cake tin.
Bake at 180 degrees centigrade for 20-25 minutes.
Turn out and cool.
For the icing, beat the ingredients together.
Spread over cake.
Decorate and serve.
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Key Ingredients: butter, castor sugar, milk, vinegar, all purpose flour, vanilla essence, cocoa, baking powder, icing sugar, chocolate