Heat oil in a stock pot. Add onion, celery, carrots, scallions, garlic. Cook over high heat for 5 to 10 minutes, stirring frequently.
Add garlic and continue cooking on high for 1 additional minute.
Add parsley, thyme, and bay leaves and and continue cooking on high for 2 additional minutes.
Add water and bring to a boil. Lower heat and simmer, uncovered, for 30 minutes. Strain. Discard vegetables.
Cool according to safe handling standards.
Notes
Other ingredients to consider: Parsnips, mushrooms, asparagus (butt ends), corn cobs, fennel (stalks and trimmings),chard (stems and leaves), celery root, marjoram (stems and leaves)