Ingredients:
3 poundsbutternut squash (about 1 large or 2 small), peeled
1 poundyellow onions (about 2 medium), peeled and quartered
2 tablespoonsextra-virgin olive oil
Kosher salt and freshly ground black pepper
3 garlic cloves, smashed and peeled
2/3 cupwalnut pieces (or chopped walnuts)
3/4 ounceParmesan, finely grated (about 6 tablespoons)
1 teaspoonapple cider vinegar
Whole-milk yogurt, for swirling on top (optional)
Directions:
Heat the oven to 400°F. Halve the squash and remove the seeds. Chop into 1- to 1 1/2–inch chunks. Add half of these to a sheet pan, along with the onion wedges. Drizzle with the olive oil and generously sprinkle with salt and pepper. Toss with your hands, breaking the onions into petals. Roast for about 35 minutes—using a spatula to shuffle everything halfway through—until the squash is tender and blistering in spots.
While that’s working, add 6 cups of water, 2 teaspoons of salt, and the garlic cloves to a stockpot and set over high heat to come to a boil. When the water is boiling, add the remaining squash and cook for about 10 minutes, until the squash is soft. At this point, add the walnuts and cook another 1 minute to soften. Turn off the heat.
Use a slotted spoon or spider to transfer the squash, garlic, and walnuts to a blender. Pour the squash broth from the pot into a heatproof measuring cup (you should have about 4 cups). Blend the squash mixture until a smooth-ish purée forms. Add 1 cup of squash broth and blend. Add the Parmesan and blend. Taste and add more cheese if you want. Pour the soup into the stockpot.
When the squash and onion are done roasting, transfer those to the blender and add 1 1 1/2 cups of squash broth. Blend until smooth. Pour into the stockpot. Add another ½ cup of squash broth to the blender and blend (this captures all of the soup that was stuck to the sides). Pour this into the pot, too.
Stir the vinegar into the soup. Thin out with more broth if you want, then taste and adjust with more vinegar, salt, and/or black pepper. At this point, you can stick in the fridge or freezer—or serve right away, drizzled with yogurt if you’d like.