Heat olive oil in a saucepot over medium heat.
Add onions and garlic. Cook for 5 minutes or until softened.
Stir in the remaining ingredients with a wooden spoon.
Allow the sauce to simmer for 15 minutes.
Use an immersion blender to puree the sauce. If you don’t have an immersion blender, pour the sauce into a regular blender and blend until smooth.
Let the sauce cool to room temperature. Serve immediately or refrigerate for one month.