1) Puree can of tomatoes. 2) Saute onion in a small amount of oil until golden brown. 3) Add garlic and cook for 1-2 minutes longer. 4) Add tomatoes, sugar, vinegar and mustard. Simmer until thick. 5) Season to taste with salt. 6) Blend or puree mixture in a food processor. (This step is optional, but it allows the ketchup to be squeeze out of the bottle better.) 7) Cool and place in a glass jar. 8) Keep refrigerated and use as needed.