Put the mashed bananas in a bowl and leave out for half an hour to oxidize – this will make them browner and add to the colour. Or if you are in a rush, just mash the bananas and get to baking the loaf.
Line and grease a 900g loaf tin and preheat the oven to 180°C/ Fan 160°C/ Gas 4.
Add the butter and caster sugar to the banana and mix till combined, then add the salt and thyme leaves, reserving a few to sprinkle over at the end. Now pour in the olive oil and milk and mix through. Add the sifted flour and fold through until you have a smooth cake batter.
Pour the mixture into the tin and level off with a few sharp taps, add the two slices of banana, cut-side up, and bake for 50 minutes to 1 hour, covering loosely for the last 15 minutes to stop the top browning too much. You will know the cake is ready when a skewer inserted comes out clean.
Meanwhile, make the caramel by adding the sugar in an even layer into the base of a pan, on medium to low heat, and watch as the sugar turns to caramel, stirring it occasionally. As soon as the sugar melts, add the butter. If you find it seizing, don’t worry, just keep stirring over a very low heat and the caramel will come together. As soon as the butter has melted, add the cream. Cook on a low heat for two minutes till you have smooth caramel. Take off the heat.
Remove the cake from the oven and leave to cool in the tin for 10 minutes, then take out and leave to cool on a wire rack.
As soon as it has cooled enough, drizzle over the caramel. If you find it has become too stiff, warm through gently and then drizzle. You will have caramel left over but not to worry, because we all need a little extra caramel and it’s perfect served on the side for anyone who wants some more to pour over. Sprinkle with a few thyme leaves, if you like.