This is such a lovely version of an upside-down cake, from its brown sugar batter and buttermilk to keep it light, to the bananas that caramelise during cooking on the base of the pan. For the best results, make sure you use small bananas or lady finger bananas.
1.Preheat oven to 180°C/350°F. Grease a 12cm x 23cm (4¾-inch x 9¼-inch) loaf pan; line base with baking paper, extending the paper 2cm (¾ inch) over the long sides.
2.Spread walnuts on an oven tray; roast for 5 minutes or until nuts are fragrant and lightly golden. Cool. Process until ground finely.
3.Peel bananas; halve lengthways. Drizzle base of the pan with butter; sprinkle with brown sugar. Top with banana, cut-side down, slightly overlapping.
4.Beat eggs, caster sugar and vanilla in a small bowl with an electric mixer for 5 minutes or until thick. Fold in sifted flour and cinnamon, then ground walnuts, buttermilk and extra butter. Carefully pour mixture over banana in pan.
5.Bake cake for 50 minutes or until a skewer inserted into the centre comes out clean; cover cake loosely with foil if it starts to over-brown. Leave cake in pan for 5 minutes before turning onto a wire rack to cool. Serve warm.
Do ahead Store cake in the fridge for up to 3 days; stand at room temperature for 30 minutes before serving. Not suitable to freeze.
Serving suggestion Serve with thick cream or ice-cream and roasted or candied walnuts.