Plug in a large (10 quart) kettle and put to 200 degrees or place a large pot on a stove top over medium heat
Pour karo syrup & sugar into the pot or kettle, stir over heat until the sugar is melted
Once sugar is melted, put cream & condensed milk in a double broiler. I use a glass bowl placed over a small sauce pan of simmering water. Warm up the cream mixture for 5 minutes.
After 5 minutes, turn heat up to 250 degrees on the kettle. Put 1/2 cup of cream mixture into the sugar mixture and stir. Let it simmer for 5 minutes before adding another 1/2 cup of cream to the sugar mixture. Repeat until all the cream is added.
Once all the cream is added, put in a candy thermometer and cook until soft ball stage (234 degrees)