Preheat oven to 180°C.
Beat butter and sugar together until the mixture becomes light and creamy.
Add the egg and mashed bananas, beating thoroughly.
Sift flour and salt together and add alternately with milk to creamed mixture.
Add walnuts and essence.
Pour into a greased 23 cm loaf tin and bake for 1 hour.
Leave in tin for a few minutes before turning out onto a wire rack to cool.
Serve with butter.