While the vegetables are roasting, get the rest of your ingredients ready to add to the stock pot.
Transfer the roasted vegetables to a large stock pot and add all of the remaining ingredients, including the reserved onion skins and the water, and stir to combine.
Bring broth the broth to a boil, then reduce to simmer and cook, partially covered for 1½ hours.
Let cool partially before straining broth through a metal strainer or cheese cloth into suitable glass storage containers.
Either use immediately or store in the refridgerator for up to a week or in the freezer for up to a few months.