Pour the sugar into a large pot and heat it over medium heat, stirring gently with a whisk as it melts. If you use very coarse cane sugar, you can add 2 tablespoons of water to the sugar, but only if it is hard to melt.
200 g white or cane sugar
At first, small lumps will form, but it does not matter; keep stirring, and slowly all the sugar will melt.
Try to keep the edges of the pot clean, possibly using a silicone spatula to move the sugar crystals that form on the sides of the pot.
When the sugar has melted, stop mixing it with the whisk and let it cook, on a lower flame, until it turns a nice amber color. If you have a candy thermometer, use it to keep an eye on the temperature, which should not exceed 345°F.
When the caramel is ready, add the butter all at once. The caramel will bubble furiously for a few seconds (this is the reason why want to use a large pot), then the butter will melt and everything will go back to normal. Mix the caramel butter with a whisk, and when all the butter is incorporated add the cream and stir some more.
180 g cold butter, cut into cubes, 250 ml whipping cream
At this point, you should have a velvety caramel sauce, to which you can add some fleur de sel.
1 pinch fleur de sel (optional)
Allow the sauce to cool for about ten minutes, then pour it into a clean glass jar.
Should there be lumps of sugar, which is not desirable, but possible, you can pour the sauce through a strainer, before transferring it into the jar.
You can keep the caramel sauce in the fridge for up to two weeks, but please reheat it a little before serving or using it in other recipes.