This soup is friendly to many vegetal additions — diced potatoes or zukes, added with the carrots and celery, or a bag of baby spinach stirred in near the end. It also takes kindly to a garlicky smoked sausage — kielbasa, say, or even the lowly frankfurter — diced and added in the middle of cooking.
Paired with corn bread, it's a delicious and comforting meal for a fall or winter evening.
Yields 8-12 cups
Heat oil in a wide sauté pan over medium-low heat, then sauté onion until translucent, about 5 minutes.
Add celery, carrots, and garlic, and sauté until vegetables soften a bit, about 5 more minutes.
Add the tomato sauce, salt, lentils, broth, bay leaf, thyme, and 2 cups water, and stir. Simmer soup over very low heat, partially covered, for an hour, stirring every now and again to keep it from sticking. (Add the kielbasa, if using, after 45 minutes.) Add water if soup looks like it's drying out.
When the lentils are nice and creamy, stir in the vinegar, then taste the soup, adding more vinegar or salt if the flavor needs brightening.