Add olive oil to a medium pot and place over medium-low heat. Stir in onions and garlic, cooking for about 20 minutes or until the onions have begun to reduce and caramelize.
Add the remaining ingredients and turn the heat down to low. Continue cooking for about 20 minutes, or until a thick, jam-like consistency is reached. Pour in a jar and seal tightly. Keeps in the fridge for about a week.