Roasted Squash Soup with Chili and Buttermilk

Roasted Squash Soup with Chili and Buttermilk
Serves 6

1 3-pound butternut squash, peeled, seeded, and cut into ¾-inch cubes (about 12 cups)
3 tablespoons olive oil
Salt and pepper
2 large onions, chopped (about 3 cups)
¾ teaspoon dried or 1 teaspoon minced fresh thyme
1½ teaspoons chili powder
3 garlic cloves, minced
6 cups low-sodium chicken or vegetable broth
¾ cup buttermilk, or more, to taste

Set the oven rack in the middle position and heat oven to 425 degrees. In a large bowl, toss the squash and 1 tablespoon of olive oil to coat. Add ½ teaspoon of salt (or to taste) and pepper to taste, and toss again to distribute the seasonings. Line a large rimmed baking sheet (roughly 18 by 13 inches) with foil, spread the squash evenly in a single layer, and roast until very tender, about 40 minutes, shaking the pan to turn the squash halfway through cooking time. Remove the squash from the oven and cool for 5 minutes.

Meanwhile, in a large saucepan set over medium heat, heat the remaining 2 tablespoons oil until shimmering. Add the onions, thyme, and ½ teaspoon of salt and cook, stirring frequently, until the onions are translucent and lightly golden, about 8 minutes. Add the chili powder and continue to cook, stirring frequently, until fragrant, about 1½ minutes. Add the garlic and continue cooking, stirring frequently, until fragrant, about 40 seconds. Add the broth and roasted squash and stir to distribute.

In a food processor or blender, puree mixture (working carefully and in batches, if necessary) until smooth. Return puree to pot, add buttermilk, and heat on medium-low, stirring occasionally, until soup is heated through. Taste soup and adjust seasoning with pepper and salt, if desired, and serve at once.