Add olive oil to a large stockpot and heat over medium-high heat.
Add onions, garlic, carrots, and celery to the heated olive oil and sauté for 5 or 6 minutes, or until the flavour is released.
Add enough water to cover the vegetables, followed by thyme, rosemary, bay leaf, parsley, and peppercorns.
Heat mixture over medium-high heat until it just about boils, and then reduce heat to low-medium.
Give it a quick stir and simmer, uncovered, for about an hour. (The exact amount of time doesn’t matter – the longer it simmers, the better the flavour will be).
Place a colander over a large pot in the sink. Carefully pour contents of stockpot into the colander to separate out the solids from the liquid.
Discard the solids and allow liquid to cool completely before transferring to freezer-safe storage containers, then freeze until ready to use.
Serving Size cups