Pre-heat oven to 180°C / 160°C fan assisted and line a 20x30cm (8×11 inch) rectangle baking tin with parchment paper.
With an electric mixer or by hand, cream together sugar and butter. Add the mashed banana and eggs then mix until combined.
Add the yoghurt, vanilla and salt and mix until combined.
Finally, add the flour and mix just until combined, scraping down the sides of the bowl as needed.
Pour batter into prepared baking tin and bake until a knife or skewer inserted into the middle comes out clean, about 30 minutes.
Leave to cool in the tin on a wire rack. Once cool, you can remove sponge from the pan and turn it over on a cutting board then carefully peel the parchment away from the cake. Return the sponge to the tin (with or without the parchment paper).
Use the handle of a wooden spoon (or something similar, roughly the circumference of a pencil) to poke 4 rows of 6 holes along the cake almost to the bottom of the pan.
Spoon the caramel from the tin directly onto the cake then use a spatula or the back of a large spoon to spread it evenly over the top.
Serve portions of the traybake with large dollops of whipped cream, a sprinkling of shaved dark chocolate and a slice or two of fresh banana.
Store the cake in the fridge covered with clingfilm or re-usable food wraps for up to 5 days. Allow to come to room temperature before serving for the best flavour.