Prepare your jam jar by washing and sterilizing the jar and lid. Keep in hot, but not boiling water until ready to use.
Add all the ingredients to a large saucepan and stir to combine.
Heat the saucepan on medium-high and allow the mixture to cook, stirring occasionally.
Continue to cook, stirring and mashing the rhubarb as you go, until the mixture thickens significantly to a jam-like consistency. Approximately 15 – 20 minutes.
Remove the jar and lid and thoroughly dry. Ladle the jam into the jar and screw the lid on well. Place in a pot of boiling water for about 10 minutes. Allow to cool completely to room temperature before refrigerating.