1 large butternut squash, peeled and cubed (seeds removed)
2 potatoes, peeled and chopped
3 tbsp. extra-virgin olive oil
Freshly ground black pepper
1 tbsp. butter
1 onion, chopped
1 stalk celery, thinly sliced
1 large carrot, chopped
1 tbsp. fresh thyme, plus more for garnish
1 qt. low-sodium chicken broth
Preheat oven to 400º. On a large baking sheet, toss butternut squash and potatoes with 2 tablespoons olive oil and season generously with salt and pepper. Roast until tender, 25 minutes.
Meanwhile, in a large pot over medium heat, melt butter and remaining tablespoon olive oil. Add onion, celery, and carrot and cook until softened, 7 to 10 minutes. Season generously with salt, pepper, and thyme.
Add roasted squash and potatoes and pour over chicken broth. Simmer 10 minutes, then using an immersion blender, blend soup until creamy. (Alternately, carefully transfer batches of the hot soup to a blender.)