Heat oven to 200C/180C fan/gas 6. Prepare a muffin tin by thoroughly buttering and lining with cases. In a bowl, mash three bananas, then stir in 50g yogurt. In another bowl, sift in the flours, baking powder, cardamom and a pinch of salt, and stir to combine.
Add the eggs and sugar to the bowl of a stand mixer, then whisk until pale and frothy – about 3 mins. Slowly pour in the melted butter in a steady stream, then add the vanilla. Turn the speed down, then add the flour mixture, 2 tbsp at a time, alternating with the yogurt and banana mix, until everything is incorporated. Mix in the walnuts for no longer than 20 seconds. Divide the mixture between the muffin cases. Bake for 25-30 mins or until a skewer inserted comes out clean.
Meanwhile, make the salted caramel by heating the butter, cream and sugar in a non-stick pan until simmering. Remove from the heat, then add the salt – you want enough to pique the sauce, but it shouldn’t taste salty.
Once the muffins are cooked, remove from the oven and leave to cool on a wire rack. Whip the cream to soft peaks, fold through 2 tbsp yogurt and slice the final banana. Spoon or pipe the cream onto the muffins. Top with the sliced banana and drizzle with salted caramel.