Allow the caramel sauce to cool thoroughly — it doesn’t have to become cool; just tepid will do; it just shouldn't be warm when you touch it. This should take approximately an hour (it depends on your local temperature!). To facilitate faster cooling, you can place the glass measure (or whatever pan you have used) it under a fan, or close to an air conditioning duct, or in a bowl of ice water. Stir it every now and then too.
Preheat the oven to 175ºc (350ºF) 20 minutes before you start baking. In fact when you know that the Caramel sauce will require another 20 minutes to cool, you can start prepping for the cake.
Equipment: One 23 by 5-cm (9 by 2-inch) cake pan. To prepare the pan, use a bit of butter to secure the bottom with a circular parchment paper, then spray the side and bottom with baking spray that has flour, or grease it with oil or butter and dust with flour. Use a cake strip on the outside of the pan, or fold a double-sheet newspaper into a 5-cm (2-inch) strip (I got 8 sheets of paper when I folded it) and wrap it around the outside of the cake pan with a thick cotton string. I had to use two big strips of newspaper (that overlapped) to cover the circumference. You could also use a long thick towel, that is is soaked in water then wrung. Secure it with a thick cotton string. For the caramel sauce keep ready a heatproof glass measure that is coated thinly with butter or cooking spray, a medium saucepan or any pan with a side that is high (to keep the hot splashes of caramel away from your hand). When you know that the Caramel sauce will require another 20 minutes to cool, you can start prepping for the cake.