Put the cake pan in the hot oven while you’re making the caramel. In a small heavy-bottomed pot, heat sugar until it is melted and turns into an amber-coloured caramel, stirring only as needed to even out dark spots. When caramel is almost ready, remove the cake pan from the oven, and once the caramel reaches the desired colour, immediately pour the caramel into the hot cake pan, tilting the pan around to spread out the caramel, making sure it covers the entire pan surface. If there are large bubbles, pop them with a spatula or a spoon. Set aside to cool. (If the sugar hardens before you can evenly spread out the caramel, put the cake pan on the stove on the lowest heat setting to re-melt the sugar.)