Melt the sugar and butter in a saucepan over a low heat without stirring.
Once the sugar has melted, turn up the heat and bring to the boil for 4-6 minutes, or until it turns a deep caramel colour. Pour the caramel into a 23cm cake tin with a solid base, or a frying pan with oven proof handles and spread the caramel out quickly with the back of a warm spoon.
Slice the bananas into 2cm-thick slices, arrange in the tin carefully in a circular pattern and sprinkle with a little sea salt.
Cut the pastry into a circle 3cm larger than the tin. Lay on top of the bananas and tuck the edges down inside the tin.
Bake for 25-30 mins until the pastry is risen and cooked through.
Leave the tarte to cool in the tin for 5 mins before carefully turning out onto a large serving plate.