In a heavy-bottomed saucepan, add the 2 cups of granulated sugar. Over medium heat, continuously stir the sugar with a wooden spoon until it begins to melt. The sugar will clump initially but continue stirring until it melts completely and turns a deep amber color. Be careful not to let it burn!
Once the sugar has melted, carefully add the 12 tablespoons of unsalted butter. The mixture will bubble up vigorously, so take caution. Stir until the butter is completely melted and incorporated into the caramel.
Next, slowly pour the 1 cup of heavy cream into the caramel mixture. Again, it will bubble up, so add it gradually and stir continuously until smooth.
Remove the saucepan from heat and stir in 1 to 2 teaspoons of fleur de sel or Maldon sea salt flakes. Taste and adjust the salt according to your preference.
Let the salted caramel sauce cool in the saucepan for about 10 minutes before transferring it to a storage container. The sauce will thicken as it cools.
