Cooking oil spray, to grease
2 x whole small sweet potatoes, about 150g each
180g peeled very ripe bananas
100ml extra virgin olive oil
50g natural yoghurt
1 free-range egg
1⁄2 tsp fine salt
120g plain flour
80g wholemeal plain flour
3 tsp baking powder
120g caster sugar
1⁄2 ripe banana, sliced lengthways
Preheat oven to 170°C fan-forced (190oC conventional). Grease a 24 x 13 x 6cm loaf tin with cooking oil. Line base and side with baking paper, allowing long edges to overhang by 5cm.
Place unpeeled sweet potatoes on an oven tray. Bake for 55 mins or until very tender. Set aside to cool for 30 minutes or until room temperature.
Cut 1 potato in half and scoop out flesh, transfer to a large bowl. Reserve remaining potato for garnish.
Combine banana and potato until a smooth puree forms.
Whisk oil, yoghurt, egg and salt in a separate large bowl until just combined.
Sift flours and baking powder into a separate large bowl, returning husks from wholemeal flour back to flour mixture.
Put banana and sweet potato mixture in the bowl of an electric mixer, add sugar and beat with a paddle attachment on medium
speed until incorporated. Add oil mixture, beat on low speed until combined. Add flour mixture and beat for 2 minutes or until combined.
Spoon the batter into prepared tin and smooth surface.
Cut remaining sweet potato in half. Set aside one half for another use. Peel remaining half and thinly slice into bite-size pieces.
Top cake batter with sliced banana and sweet potato pieces. Bake for 55 minutes or until cooked when tested with a skewer. Set aside to cool in tin for 20 minutes, then turn out on a wire rack to cool completely. Transfer to a platter and serve.