Add the sugar to your saucepan and heat over medium heat, stirring frequently. Continue to heat the sugar until melted and smooth.
Add the room-temperature butter 1 tablespoon at a time (it will bubble up), whisking until fully melted and incorporated into the sugar.
Remove from heat and slowly pour in the room-temperature cream, whisking as you pour it.
Allow to cool for 15 minutes at room temperature, then transfer to a mason jar or other wide-mouth container (see notes) and store in the fridge for up to 1 month.
Notes
Note: the caramel sauce will be liquid when warm but will solidify in the fridge. Be sure to store it in a container that you can heat in the microwave and/or scoop from if needed. This makes about 1.5 cups of caramel sauce!