Place a candy thermometer to a medium saucepan. Stir together sugars, butter and cream. Cook on medium heat until it comes to a boil. Let simmer for a few minutes. I let it reach 325 degrees then take off heat. Remove from heat and add vanilla and salt.
Let cool and enjoy! Keep refrigerated..
It may take between 15-20 minutes to bring sauce to temperature, different stove tops vary.