serves 8
For squash soup
3/4 stick (6 tablespoons) unsalted butter, cut into pieces
1 medium onion, halved lengthwise and thinly sliced crosswise
1/2 teaspoon salt
2 lb yellow summer squash, halved and thinly sliced
2 carrots, thinly sliced
1 yellow-fleshed potato (1/2 pound), peeled, halved, and thinly sliced
4 cups chicken stock or reduced-sodium chicken broth
For pistou
3/4 cup loosely packed fresh mint leaves
1/2 cup loosely packed fresh flat-leaf parsley sprigs
1 large scallion, chopped (1/2 cup)
1/4 cup extra-virgin olive oil
2 tablespoons water
1/4 teaspoon salt
Make soup:
Melt butter in a 6- to 8-quart wide heavy pot over moderate heat, then cook onion with salt, stirring, until softened, about 8 minutes. Add squash, carrots, potato, and stock and bring to a boil. Reduce heat, then simmer, partially covered, until vegetables are very tender, about 20 minutes. Remove from heat and cool soup, uncovered, 10 minutes.
Working in batches, puree; soup in a blender until smooth (use caution when blending hot liquids) and transfer back to pot. Or, you can use an immersion blender to do the job right inside the pot. Thin with water if desired; simmer 3 minutes more. Season with salt.
Make pistou:
while vegetables simmer: Pulse mint, parsley, and scallion in a food processor until finely chopped. With motor running, add oil in a stream, then add water and salt, blending until incorporated.
To serve:
Swirl one tablespoon pistou into each bowl of soup.