Ingredients
2 tablespoons extra-virgin olive oil
3 anchovy fillets
2 leeks, white and pale-green parts only, halved lengthwise, thinly sliced crosswise, washed well, and drained (about 4 cups)
2 small celery stalks, cut into 1/2-inch pieces (about 2/3 cup)
Coarse salt and freshly ground pepper
1 small zucchini, cut into 1/2-inch pieces (about 1 1/2 cups)
1 small yellow squash, cut into 1/2-inch pieces (about 1 1/2 cups)
4 cups low-sodium chicken broth
1 Parmesan rind, about 1 by 3 inches
2 cans (15.5 ounces each) small white beans, such as navy, rinsed and drained
1 cup lightly packed fresh basil leaves
2 cloves garlic, smashed
1/3 cup grated Parmesan, plus more for serving
1/4 cup extra-virgin olive oil
Coarse salt and freshly ground pepper
Preparation
Soup: Heat oil in a large pot over medium heat. Add anchovies and cook, stirring, until dissolved, about 1 minute. Add leeks and celery; season with salt and pepper. Cook, stirring occasionally, until vegetables are soft and golden in spots, about 20 minutes.
Stir in zucchini, squash, broth, 2 cups water, and Parmesan rind. Bring to a boil over high heat, then reduce heat to low, cover, and simmer until vegetables are tender, about 15 minutes. Stir in beans and simmer, covered, just until warmed through, about 2 minutes. Remove rind.
Pistou: Meanwhile, pulse basil, garlic, Parmesan, and oil in a food processor to a loose paste. Season with salt and pepper.
Divide soup among bowls. Stir in pistou as desired, sprinkle with Parmesan, and serve.
