Scrub beets and trim tops and rootlets. Boil beets whole until tender. Drain and immerse in ice water to cool down. Slip off their skin and slice in 1/4 inch rounds, or quarter/ halve them into approximately the same size pieces. Combine pickling spice, sugar, salt, vinegar and water in a saucepan and bring to a boil. Reduce heat and simmer for 10 minutes. Pack beets and optional onions into a quart jar, pour hot liquid over leaving a 1/2 inch of headspace from the top.
Process by canning if desired or store directly in fridge. Try to wait 1 week before tasting!