Preheat oven to 400°F (200°C).
Toss butternut squash, apples, onion, and garlic with olive oil on a baking sheet. Roast for 25-30 minutes until tender and lightly caramelized.
Transfer roasted vegetables to a large pot. Add broth, apple cider, cinnamon, and nutmeg.
Bring to a boil, then reduce heat and simmer for 15 minutes.
Use an immersion blender to puree the soup until smooth. Alternatively, carefully transfer to a blender in batches.
Stir in heavy cream if using. Season with salt and pepper to taste.
Serve hot, garnished with pumpkin seeds if desired.