Preheat the oven to 170C Fan.

For the banana base: melt the butter in a 20 cm (8-inch) non-stick oven-proof deep frying pan. Add the sugar and heat gently until the sugar has dissolved.

Slice the bananas lengthways and arrange snuggly in a pretty layer cut side down in the pan (this is what you will see when you turn the cake out). Squeeze over a little lemon juice and remove from the heat.

For the cake topping: in a large mixing bowl, mix together the mashed banana, yoghurt and vanilla extract. Set aside.

In a separate bowl, cream together the butter and sugar with an electric beater until pale and fluffy. Add the eggs one at a time, beating well after each addition. Fold in a few tablespoons of the flour, followed by the banana-yoghurt mixture. Repeat until all of both mixtures have been added and fully combined.

Carefully spoon the mixture over the banana caramel layer and spread in an even layer. Place in the oven and cook for about 40-50 minutes - or until golden brown, firm to the touch and a skewer inserted into the centre comes out clean. Remove from the oven and leave to stand for 5-10 minutes, then turn out onto a flat plate.

Cut into slices and serve with a scoop of vanilla ice cream, if wished.