Grease and line a 22cm cake pan. Preheat oven to 190°C.
Beat butter, essence and sugar together until light and creamy. Add eggs - one at a time - beating well after each addition.
Stir in milk, lemon juice and bananas. Continue to beat for another minute. Sift self-raising flour and bicarbonate of soda together. Fold the sifted dry ingredients into the wet ingredients until well combined. Add in walnuts and stir till combined.
Transfer batter to the prepared cake pan and bake for 40-50 minutes or until cake is done when a wooden skewer inserted into the centre of the cake comes out clean.