On the stove over medium/high heat, melt sugar in a heavy bottom sauce pan. The sugar will get clumpy like sand before it melts, keep stirring and don't give up- it will melt I promise. Once melted, add in butter continually stirring until it is melted and incorporated into the sugar. Stir in heave cream and let it bubble up the side for about a minute. Turn off heat and stir in salt. It will thicken as it cools. Store in fridge.