Rhubarb Ketchup

• 3 cups chopped rhubarb (about 6–8 medium-size stalks, cut into ½-inch pieces)
• 2 yellow onions,

Combine all ingredients in a heavy pot over medium-high heat. Bring to a boil, stirring frequently. Reduce heat and simmer, uncovered, for about 1 hour. Let cool, and remove pickling spice bag. Spoon rhubarb mixture into a blender, and puree until smooth. Transfer to a sterilized glass jar with lid; store in refrigerator.