Cream butter and sugar. Add eggs, bananas, then baking soda dissolved in milk, stirring after each addition. Lastly add mixed flour and baking powder. Mix.
Bake in greased, floured baking tin at 180C/350F until skewer comes out clean - about 40 mins. Let sit in tin for 5 mins, then turn out onto rack to cool.
Hint: if banana cake browns too quickly on top and is still uncooked in the middle, placing an oven tray over the top of the cake tin will prevent it overbrowning while it finishes cooking.