Peel the vegetables and cut them in big pieces. In a large stockpot, heat the olive oil and add the onion, garlic and spices. Cook for a few min, without browning.
Add the vegetables and cook on medium to low heat for 10 min, until soft. Add the water and season with salt. Cover and bring to a simmer, and cook for 20 min.
Remove from the heat and let rest for a few hours (or even overnight in the fridge) for the flavors to develop even more. Strain the broth and use when needed. It keeps well in the fridge for a few days.