Combine all the ingredients in a large heavy pot and bring to a boil over medium heat, stirring constantly.
Continue boiling for 30 minutes.
Remove the mixture from the heat and allow to cool to room temperature. Refrigerate overnight.
Return the mixture to a boil over medium heat.
Continue boiling and stirring until the mixture reaches the desired consistency, approximately 1 hour. To test, spoon a drop onto a cool plate. Tilt the plate to see how runny the cooled mixture will be.