Cream the butter and sugar in a standing mixture (or by hand) until white and fluffy.

Add the eggs, one at a time and beat well.

Mash the bananas, then add them.  Mix in.

Heat the milk to nearly boiling.  Add the sodium bicarbonate to it.  It should become a foam when you stir it.

Add this foam to the cake batter and mix.

Add the flour and baking powder and mix gently until it becomes incorporated.

Scoop the batter into a 25cm (10  inch) diameter greased cake tin.

Bake at 180ºC ( 350ºF) for 35 - 40 minutes until a cake tester comes out clean. Start testing at about 30 minutes, as it gets dry if cooked too long.

You can decorate it with icing sugar, or chocolate or white icing, or just leave it plain.  It's good every way!