Skin tomatoes, remove stems and puree until you have 1 1/2 cups of puree’d tomatoes.
Soften onions by cooking them on low heat in corn oil until they begin to become translucent. Once onions are softened, puree them. You should have only 1/4 cup worth of puree’d onions. You may puree the garlic clove with the onion. Try to remove as much of the corn oil as possible before puree’ing the onions.
Combine all ingredients in a small sauce pan and simmer for about an hour and a half, until it begins to thicken. Remember to stir from time to time to prevent scorching.
Remove from heat and transfer the entire sauce into a blender and puree until smooth. Be careful with blending the sauce while it is hot, you may want to allow it to cool a bit first.
Place the finished ketchup into a container and refrigerate, allow at least 2 hours for the flavors to marry.