In a large pot, heat the oil over a medium high heat. Add the onions and garlic and saute until the onions are translucent about 10 minutes. Add the celery and carrots and 1/2 teaspoon each of salt and pepper. Saute the until the vegetables are soft about ten minutes.. Add the tomatoes and bay leaves and simmer uncovered over low heat until the sauce thickens, about 1 hour. Remove the bay leaves and discard. Season the with more salt and pepper to taste.(The sauce can be made one day ahead, refrigerate , rewarm over medium heat before using).