PLACE into the large bowl of a food processor enough fresh ripe Roma tomatoes to yield approximately 1 1/2 cups pureed, and one stem-removed seeded fresh jalapeno pepper; PROCESS both until pulverized.
04TRANSFER the sauteed onion and garlic roux from the saucepan into the bowl of the food processor with the tomatoes and jalapeno, submerging the into the pulverized mixture first.
05PROCESS until all ingredients until finely pureed.
06POUR pureed mixture into the same medium saucepan.
07STIR in 5 cups water, 2 teaspoons salt, 1 1/2 teaspoons crushed Mexican oregano (crush between fingers) 1/4 teaspoon finely ground black pepper, and 1 small bay leaf.
08BRING mixture to boiling while whisking; REDUCE heat to medium and cook for about 45 minutes, whisking occasionally, or until desired consistency is reached; COVER slightly vented so steam can escape; KEEP sauce warm over lowest heat, whisking occasionally until served, or reheat and stir before serving.
09POUR a small pool of warmed sauce onto chile relleno serving plate; PLACE chile relleno over sauce; TOP chile relleno with additional sauce; GARNISH as desired; SERVE.