Step 1: Trim beet tops, leaving 1 inch of stem and the roots intact to prevent bleeding. Scrub them gently under cold water.
Step 2: Place beets in a large pot and cover with water. Bring to a boil, then reduce heat and simmer for 30-45 minutes until tender.
Step 3: Drain the beets and immediately plunge them into ice water. Slip off the skins, stems, and roots with your fingers. Slice or quarter the beets as desired.
Step 4: In a separate large saucepan, combine sugar, vinegar, water, salt, cloves, allspice, and cinnamon stick. Bring the mixture to a boil.
Step 5: Pack the sliced beets (and onions if using) into sterilized glass jars. Pour the hot brine over the beets, leaving 1/2 inch of headspace.
Step 6: Seal the jars and allow them to cool to room temperature. Store in the refrigerator for at least 24 hours before eating to let the flavors develop.