Grease a large loaf tin that will fit on the lower rack of the halogen oven. Mash the bananas.
Beat together the butter, sugar and maple syrup using a hand-held electric whisk until pale and creamy. Stir in the egg, yogurt and mashed banana until evenly combined. Sift the flour and baking powder into the bowl and stir in until just mixed through. Turn into the prepared tin and level the surface. Place on the lower rack of the halogen oven and cover with foil.
Set the temperature to 175°C (347°F) and cook for 35 minutes. Lift away the foil and cook for a further 15 minutes until risen and just firm to the touch. (A skewer inserted into the centre of the cake should come out clean.) Leave in the tin for 10 minutes, then transfer to a wire rack to cool. Serve dusted with icing sugar, cut into slices.