In a large saucepan warm olive oil over low heat. Add onion and half of the salt, sauté until translucent and soft, about 5-6 minutes.
Next, pour in the mustard, vinegar, Worcestershire sauce, and molasses. Stir and follow with brown sugar and spices. Whisk thoroughly and simmer on low heat for 35-45 minutes. Remember to stir frequently to make sure that it doesn’t stick.
Allow it to cool before straining the sauce through a fine-mesh strainer to remove the onion. Store in a glass jar with lid for a week or so in the fridge or use immediately.