Wash all vegetables and herbs very well. Chop into 1-inch chunks or smaller. (The greater the surface area, the more quickly vegetables will yield their flavour.)
Heat oil in a large soup pot. Add onion, celery, carrots, leeks, and dried herbs. Stir to cook over high heat for 5 to 10 minutes until lightly golden. Add garlic and stir until fragrant but not browned.
Add cold water and bring to a boil. Lower heat and add fresh herbs. Simmer, partially covered for 30 to 45 minutes. If vegetables are in larger pieces, simmer for up to 90 minutes.
If stock is too bland, consider simmering longer. If you’ve simmered too long, your stock will be more concentrated. If it has evaporated too much, add a little more water.
Strain, cook, and store.