Tomato Basil Parmesan Soup

Ingredients

1 c. finely diced onions
3 cloves garlic, finely chopped
2 (14 oz) cans diced tomatoes, with juice (fire-roasted tomatoes are nice, but not necessary)
1 c. finely diced celery
1 c. finely diced carrots
1/4 cup fresh basil, finely chopped
4 c. veggie stock
6 T. butter
1/2 c. flour
1 c. Parmesan cheese
2 cups milk, warmed
salt and pepper to taste
cheese tortellini (optional)

Cook the onions until well browned, then add the garlic and saute for ~30 seconds. Place onions and garlic in a large crockpot.
Add the rest of the ingredients (tomatoes-veggie stock) to the crockpot. Cover and cook on low for 5-7 hrs. All the veggies should be very soft. Puree the soup with an immersion blender, or in batches in a blender or food processor. Return the soup to the crockpot and keep cooking.
About 30 minutes before serving prepare a roux by melting butter over low heat and then adding flour. Stir constantly with a whisk for 5-7 minutes. Add 1 c. of hot soup to the roux and stir until smooth. (Will cause the roux to become paste-like – keep stirring until smooth) Add more soup (up to 3 cups) to the roux, until the mixture is thin enough to pour easily back into the crockpot. Pour the soup into the crockpot. Add the parmesan and the warmed milk to the crockpot and cook on low for another 30 min.
While the soup is finishing, boil the tortellini according to the package directions, if using. Serve with the soup. (You don't want to put the tortellini *in* the soup until you serve it, in case of leftovers. If the tortellini are left in the soup then they soak up a lot of the soup and become very bloated and strange. Instead, save any leftover tortellini in a separate container and add to the soup as needed.)

To make a lower fat version of this soup, use skim milk and cut back the parmesan to 3/4 c. Don't skimp on the butter, though – the roux does not work right if you use margarine or light butter, and it's just not worth it.
If you are one of those strange people who don't like onions or garlic, you can make it without. I've been told (by someone who doesn't like onions) that it was very good that way. I'd definitely use the fire-roasted tomatoes, then, to give it a bit more flavor.
If making the soup on the stovetop (instead of a crockpot), bring the soup to a boil and then simmer until the vegetables are soft (30 min.?). Then make the roux and add it and the milk and the parmesan to the soup pot and cook until the soup is hot.
This soup also works very well with halving the recipe. Since the full recipe makes 10-11 cups, half a recipe is still plenty for a dinner for 3-4 people. Or you can make the full recipe and freeze half. Don't *double* the recipe, though, because that makes a fuckton of soup, and doesn't work out well (the proportions get weird).