Preheat the oven to 180C/350F/gas mark 4
Use two 23cm/9 inch sandwich tins.
Line and grease the sandwich tins. Sift the flour, baking powder, bicarb and salt into a bowl.
Cream the butter and sugar until light and creamy. Mash the bananas and mix into the creamed butter. Add the dry ingredients, one third at a time, alternately with the yoghurt, beating well after each addition.
Stir in the walnuts and spoon into the prepared tin. Bake the cakes for about 30 minutes. Cool on a wire rack.
