To make the tomato sauce, in a nonaluminum saucepan, heat the olive oil over medium heat. Add the onion and saute until soft and lightly golden, about 6 minutes. Add the garlic and saute for 1 minute longer; don't let the garlic brown. Stir in the tomato sauce, vinegar, red pepper flakes and salt. When the mixture just begins to bubble, reduce the heat to low and simmer for 5 minutes. Remove from the heat and set aside.