The extreme temperatures swinging this way and that keep us on our toes. One day we’re sucking down a fruit smoothie while searching for a swim suit, the next finds us adjusting the thermostat to accommodate the 20-degree dive, scrambling for a sweater, then gobbling down favorite comfort foods.

Craving hot soup when last week’s chill set in, I was determined to keep it brothy clear and full of vegetables, forgoing the calorie-bomb chowder I truly desired. (I found that swim suit — yikes!) But to give it breadth and interest, I incorporated a late-May twist with the addition of pistou. Pistou elevates a plain vegetable soup to something extraordinary. The recipe below, in fact, would be rather lackluster without the pistou.

No, pistou isn’t a misprint, or the Latin word for pesto. Pistou is a culinary word unto itself, although it shares many similarities to its first cousin pesto, and more than likely they both share the same origins. Pistou hails from the Provence region of France and is most often associated with Soupe au Pistou, which is a brothy soup, similar to the recipe below, incorporating seasonal vegetables and always pistou.

Fresh basil is essential to Pistou, but after that, all bets are off. As we’re entering fresh basil season, you’ll find plants at nurseries and groceries ready to plant in a garden or pot. I’d encourage you to plant your own; it’s one of the least temperamental edibles I grow, as long as it gets plenty of sun, is regularly pinched back and is never exposed to frost.

Certainly today’s cook takes numerous license with generic pestos, but most of us are in accord that a classic Italian basil pesto incorporates fresh basil, garlic, olive oil, pine nuts and the best Parmesan your purse will allow. Like pesto, pistou is served with pasta dishes, grilled meats and seafoods, or used as a savory base for crostini or bruschetta.

But I’ve yet to see defined a classic version of pistou. Some recipes don’t incorporate cheese; others omit the tomato. Some recipes incorporate more tomato than basil, and some add lemon juice. Some pistous are paste-like, others thin. Even Patricia Wells (cookbook author, food critic, and often considered the doyenne of the Provence table) has penned different versions. The main difference separating pesto from pistou, from what I gather, is that nuts are never incorporated into pistou. If you decide to embrace the free-wheeling spirit of pistou and incorporate nuts, call it pesto.

Even when—if?—the temperatures settle into a more summertime pattern, this is a marvelous kitchen-sink recipe, perfect for showcasing summer’s seasonal delights. Fresh green beans, peas, turnips, chard, potatoes and any variety of squash would be a marvelous substitution for any of the vegetables listed below.

The following recipe was adapted and modified from a recipe from Saveur and insures there is plenty of pistou to pass; the more pistou the better. A fresh baguette is the only accompaniment you will need, and leftovers taste better the next day.

A friend recently told me a joke: Fool me once, shame on you. Fool me twice, shame on me. Fool me 565 times, and you’re the weather forecaster. No doubt.

Yield: 6 servings
Active Time: 40 minutes
Cooking Time: about 40 minutes

Ingredients for the Pistou:

4 cups basil leaves, washed and spun dry
1 cup grated Parmesan Reggiano
1/4 cup extra-virgin olive oil
1 teaspoon chopped garlic
1 ripe plum tomato, cored and coarsely chopped

Instructions for Pistou:

In a food processor or blender, process basil, Parmesan, olive oil, garlic, and tomato, with on and off pulses, until well combined. Season to taste with kosher salt and freshly ground pepper. Set aside or refrigerate until ready to use.

Ingredients for the soup:

1/4 cup extra-virgin olive oil
2 teaspoons finely chopped garlic
1 1/2 cups peeled, chopped carrots
1 cup chopped celery
2 cups chopped onions or leeks
1 cup diced zucchini
4 cups thinly sliced cabbage or kale
8 cups vegetable or chicken stock
1 (28-ounce can) whole, peeled canned tomatoes, chopped, with juice; or 4 large ripe tomatoes, cored and chopped
1/3 cup small dried pasta, such as ditalini, or broken dried spaghetti
1 (15-ounce) can cannelini beans, drained and rinsed
1 teaspoon red pepper flakes
1 recipe for pistou

Directions for the soup:

1. In a large heavy-bottomed pot or Dutch oven, heat oil over medium heat. Stir in garlic, carrots, celery, and onions or leeks. Cook, stirring occasionally, until just tender, 12-15 minutes.
2. Stir in zucchini and cabbage or kale. Cook, stirring occasionally, with a pinch of kosher salt until wilted, 4-5 minutes. Stir in stock and tomatoes, and bring to a boil. Add pasta and cook until al dente, checking cooking instruction on pasta packaging for cooking time.
3. Mash half the beans with a fork. Stir into soup with remaining whole beans and simmer until heated through. Season with kosher salt and red pepper flakes. Ladle soup into bowls and serve with pistou stirred into the soup or dolloped on top.

Peggy Lampman is a real-time food writer and photographer posting daily feeds on her website and in the Food & Grocery section of Annarbor.com. You may also e-mail her at peggy@dinnerfeed.com.