Sopa de chayote (Vegetable Pear Soup)

Chayote (also known as vegetable pear) is a vegetable native to Mexico and Central America, in the same family as zuchini. One day I had some chayotes I needed to use, so I decided to use them in a soup, adding chicken broth to them. I really liked the result, with the consistency similar to having added potato, so now I have added this soup to my repertory. As with other recipes, the amounts are approximate, since I don't usually measure.
Ingredients
2 chayotes, sliced thinly
1 cup medium onion, chopped
4 L chicken broth
1 tsp dried tarragon
1/4 cup balsamic vinegar
1 tbsp unsalted butter
On a soup pot on medium heat, melt the butter until the bubbling subsides. Sauté the onion until it is transparent. Add the tarragon and let it sauté for a few moments. Enjoy the aroma.
Add the chayote slices, mix well, then let it sauté for about 5 minutes.
Add the chicken broth and bring to a boil. Lower the heat to low, add the vinegar, and let the soup simmer for 30 minutes.
Transfer the soup to a blender and blend until smooth. (You might have to do this in batches.) Return the soup to the pot, correct the seasoning and let it heat up for 5 minutes. You can add some fresh ground pepper, to taste.
Serve hot, garnished with croutons and crême fraîche.
Notes
The flavor is much better if you use left-over champagne instead of balsamic vinegar.
I usually use Campbell's chicken broth, which makes the broth 900ml (about 3 3/4 cups) instead.
I like to change the herbs on different servings, using dill, thyme or Herbs de Provence.
Because of its consistency, chayote soup is perfect with combining with other potato-based soups, like roasted red pepper soup, in a "rainbow soup" presentation (serving two or more separate soups in the same plate without mixing).