In a large pot, add the olive oil (or sub water) and sauté diced onion and garlic over medium heat until the onions have been cooked.
Add the remaining ingredients to the pot and simmer for about 30 minutes, then remove bay leaves.
Let cool for a few minutes, then add the mixture to a large blender or food processor and blend until smooth. Note: This may be ideal to do in small batches depending on your equipment. I would also hold the lid down firmly just in case pressure builds up and it decides to fly off. No one wants a messy kitchen!