Heat the oil in a medium sized saucepan over medium high heat. Sauté the onion and celery until the onion is translucent. Depending on your stove and pan, 5 to 8 minutes.
Add the rest of the ingredients, whisk or stir together and bring to a boil.
Cover and reduce the heat to low and simmer until the sauce is the desired thickness. This can take up to 15 minutes or more.
When done, remove from the heat and let cool. If you are not using all the sauce for one meal, remove what you are going to use so you don't contaminate the unused portion.