Combine all ingredients except vanilla in a medium sauce pan. Bring to a simmer over medium-low heat, stirring occasionally to keep it from sticking and scorching. Simmer for 25-30 minutes or until thickened and a rich dark brown in color.
Remove from heat and stir in vanilla.
Store in the fridge for 2-3 weeks. To preserve longer than this, ladle into freezer jars and freeze.