There is a children's story, a parable of sorts called "Stone Soup". A hungry peddler comes into a town where there isn't much food, and carries a sack over his shoulder. In the sack is a large stone; he stops at shops asking for food, and is denied. He then suggests that he will be making Stone Soup and would like the townspeople to join him. He fills a pot with water, deposits the stone and then proceeds to extol the virtues of Stone Soup, but then says, "this soup would be so much better with an onion.....a piece of meat.....a carrot....." you get the picture, by the time he's done there is a thick soup in the pot filled with the contributions of everyone in the town and they ate heartily. Stone soup is something that comes out of my refrigerator on a monthly basis, when the leftovers are crowding out everything else in there!
This recipe is a great way to use up leftovers, it's not written in stone (sorry for the pun!), so you can substitute your favorite leftovers, broth flavors, and meats.
The French call this mixture of onion, carrot and celery a mire poix; it sautes for 3 to 5 minutes until the vegetables are softened, and the onion releases some oil and becomes fragrant. You'll need about 2 tablespoons of good olive oil, and about 1 1/2 cups of the mire poix. Yes, that IS a red onion--leftover from a spinach salad. I added 1/4 cup tomatoes because I had them leftover and 1 teaspoon dried thyme and dried sage leaves.
We had plenty of flap meat leftover from our grilling night, I just cut it into small pieces and added it to the saute. If you have leftover rotisserie chicken, seafood, any type of protein, you will need 2 to 3 cups.
Demi-Glace is a deep flavored concentrate, which can be reconstituted with water. You will need about 5 cups of broth, or stock. Use what you have on hand, if you are using beef, use a beef broth, chicken, chicken broth. Bring to a simmer for 20 minutes.
When the broth comes to a boil, add 2 cups of greens; either spinach, chard, escarole, even romaine lettuce works here---trim stems on romaine and cut into 1-inch pieces. Simmer another 10 minutes.
Leftover pasta from a previous dinner. Make sure it is cooked, otherwise it will absorb all the broth. Cut it into smaller pieces and add about 10 minutes before serving. I also added the rind from Parmigiano Reggiano diced into small pieces with the broth. The rinds become soft and pliable, and add saltiness and a lovely flavor to the soup.
Voila! In less than an hour a hearty stone soup; we served this with leftover home made pizza, but corn muffins, foccacia, or bread makes this a great meal.