Hot and Sour Cabbage Soup

Soups can be beautiful in person, but unlike most solid foodstuffs, they can be extremely difficult to "style" for photographs. Soups that are a solid color and smooth in texture are usually the most photogenic. Soups that have a lot of components, such as lentil soup or chili, tend to look overly busy, like a jumble of random, mushy ingredients. This soup fell into the unphotogenic category the first few times I made it, since the onions and cabbage - its main components - just turned sort of brownish. It tasted good, but I didn't want to take a picture. Then, in a moment of food blogging epiphany, I decided to use red onion and red cabbage. Suddenly, the soup looked as vibrant and delicious as it tasted.
The soup is originally from a Sara Moulton recipe and I think that I first copied it down during one of her shows, back when she was still on the Food Network.
It is very easy to make and involves minimal prep work. For anyone who has ever chopped up a cabbage, you probably know that it is one of the easiest veggies to work with after you cut out the core. The "hot" part of the soup comes from the red pepper flakes and the head level can easily be adjusted by eliminating a quarter teaspoon or so. The "sour" part comes from the balsamic vinegar, which adds a very slightly sweet-sour taste to the soup. Choose a good vinegar, since you'll be able to taste it in the finished dish.

Hot and Sour Cabbage Soup
1-2 tsp vegetable oil
1 large red onion, quartered and thinnly sliced
2 garlic cloves, minced
1/2 - 3/4 tsp red pepper flakes
1/4 cup balsamic vinegar
2 tbsp brown sugar
6 cups finely sliced red cabbage (about 1/2 large cabbage)
1 can (15-oz) plum tomatoes, drained and chopped
6 cups vegetable stock
Salt and pepper, to taste

In a large pot or dutch oven, heat vegetable oil over medium heat and cook the onions until just tender, about 5 minutes. Add in the garlic and red pepper flakes, stirring for and additional minute.
Add all remaining ingredients and cover. Bring to a boil, then reduce the temperature and simmer until cabbage is tender, about 1 hour.
Season with additional salt and pepper before serving.

Serves 6-8