Mix sugar, corn syrup 1 cup of the cream in a large bowl.  Once the mixture is smooth and well combined pour into a large heavy sauce pan.  Add the butter.  Cook over medium/low heat until mixture begins to boil. Wash the sides of the pan with a wet pastry brush, if sugar crystals are present.  Stir constantly.  When butter has melted and mixture has come to a rolling boil, slowly add remaining cream trying not to let the mixture stop boiling.

Clip on a candy thermometer, turn heat to low. Stir constantly and cook until caramel reaches 234F.  Drop a small amount of the hot caramel into a bowl of cold water.  If you can pick up the caramel and form a soft ball the caramel is finished.