Pre-heat oven to 180°C conventional (160° fan bake). Grease a deep 20cm round cake tin and line the base with baking paper.
Beat butter and sugar until light and fluffy.
Beat in eggs one at a time. Stir in bananas and vanilla essence until combined.
Mix baking soda and milk together before stirring into the banana mixture. Sift in flour and baking powder, fold into the mixture until combined.
Spoon mixture into prepared tin and smooth the top. Bake for 40-45 minutes until cooked (insert a clean skewer, if it comes out clean it is cooked). Stand for 5-10 mins before inverting onto a wire rack to cool. Ice with chocolate icing when cold.
Icing: Mix Chocolate Icing Sugar, butter and 1 Tbsp boiling water at a time until combined, adding more hot water until icing is a spreadable consistency. Smooth over the top of the cake.