Peel and finely chop the onions. Peel and finely grate the ginger. Crush the cardamom, remove the seeds, and crush the seeds in a mortar. Add the onions, ginger, cardamom, vinegar, sugar, raisins, cinnamon, bay leaves, and salt to a pot. Simmer gently for 15-20 minutes, stirring occasionally.
Rinse the rhubarb, and remove the fibrous strands if necessary. Slice the rhubarb into 1-2 cm (approximately 1/2 - 3/4 inch) pieces. Add to the chutney and cook for 5 minutes. The rhubarb should be soft, but not falling apart. Fill the prepared jars to the brim with the chutney. Seal tightly, and cool upside down for 10 minutes. Turn right side up and cool completely.