Prepare your ingredients and keep them near the pan you are using. Cut the butter in tablespoon pieces and measure out the heavy cream and salt. Make sure the butter and cream are at room temperature before using.
Pour 1 cup of granulated sugar into a relatively deep, heavy bottomed saucepan.
Heat the sugar over medium heat until it melts, stirring constantly with a wooden spoon. It will clump up as it melts, but just keep stirring.
Once the sugar has all turned to liquid, keep stirring a minute or so until it turns a light amber color. It can burn very easily, so as soon as it changes color, go to the next step.
Add the butter to the melted sugar, stirring constantly. It is going to angrily spit at you, so be careful! Stir until the butter is completely melted and incorporated.
Add the cream into the butter and sugar. Pour the cream into the mixture in a steady stream while stirring constantly. Be careful of the spitting!
Stop stirring and let the mixture boil for one minute.
Remove the mixture from the heat and stir in the salt. Start with 3/4 teaspoon, taste, (carefully - it is hot!) and add a little more if desired.
Let the mixture cool slightly in the pan, about 8-10 minutes.
Pour the mixture into a heatproof container. A jar like the kind you use for making jam is a good choice.
Let the sauce cool in the fridge. It will get thicker as it cools.
The sauce is rather thick once it is chilled. If you need it to be thinner, heat a bit of water to simmering in the bottom of a pan and place the jar in the hot water. Heat until the desired consistency.