I don't know which version you looked up, but as far as I recall from the version I used, essentially you put the chicken some carrots & possibly some swede in a pot, cover with water, bring to the boil and then simmer until the chicken is cooked - depending on weight about 1 1/2 - 2 hrs. I don't recall onion. Taking the cooked liquor you discard the original veg and then cook some fresh fine diced carrot & swede , dice off some of the chicken and serve the liquor with 3-4 pieces of carrot, swede and chicken well seasoned with salt & pepper, so that it is a delight to the eye and light on the stomach. It should be cooked quickly and lightly so to keep the freshness in, not boiled to death.
But as I say there are probably as many versions as their are cooks
Terrie, I read that this was known as the 'Jewish penicillin'