How to Make It
Heat oven to 400° F. On a rimmed baking sheet, toss the pumpkin with 3 tablespoons of the oil, ½ teaspoon salt, and ¼ teaspoon pepper. Roast, tossing once, until tender, 20 to 25 minutes.
Meanwhile, heat the remaining 2 tablespoons of oil in a large saucepan over medium-high heat. Add the leeks and cook, stirring frequently, until tender, 4 to 6 minutes. Add the roasted pumpkin, 4 cups of the broth, and ½ teaspoon salt and bring to a boil; reduce heat and simmer for 5 minutes.
In a blender, working in batches, puree the soup until smooth, adjusting the consistency with the remaining broth as necessary. (Alternatively, use a handheld immersion blender in the saucepan.) Top the soup with the sour cream and croutons and sprinkle with the paprika, if desired.