In a medium saucepan, warm the olive oil over low heat. Stir in the onion. Cook, stirring occasionally, for about 12 minutes or until translucent.
Raise the heat and stir in the fresh tomatoes. Bring to a boil. Lower the heat and simmer, stirring occasionally, for 20 minutes, or until the tomatoes are soft and liquid. Or stir base or sterile-pack tomatoes into the cooked onions and brin