Get a saucepan with a little bit of Olive Oil (2 tablespoon) in it. Add in Yellow Onion (1) which has been roughly chopped up over a medium heat.
Once it is nice and softened, add in Brown Sugar (2 tablespoon).
Add in Canned Diced Tomatoes (45 ounce) and Ground Allspice (1/4 teaspoon). Give that a good stir together.
Season with little Salt (to taste). Bring the mixture to the boil then simply reduce the temperature down to low and allow the mixture to simmer for about half an hour.
Add in Tomato Paste (2 tablespoon) and Distilled White Vinegar (1/3 cup). Give that a good stir and allow this to simmer for another five minutes.
Transfer the sauce into a food processor or a blender. Make sure that you take that little removable lid off the top of the blender allow any excess steam to escape.
Puree this until it is nice and smooth. Push the sauce through a fine sieve.