Preheat oven to 425°F (220°C) and line a rimmed baking sheet with parchment paper.
Peel and seed the pumpkin and cut the flesh into approximately 1-inch chunks.
Peel and chop the carrots into thick pieces.
Cut the onion into wedges and peel the garlic.
Spread pumpkin, carrots, onion, and garlic over the baking sheet.
Drizzle with olive oil and season with salt and black pepper.
Toss and spread into a single layer.
Roast for 30–35 minutes, turning once halfway through, until tender with caramelized edges.
Transfer the roasted vegetables to a large soup pot.
Add vegetable broth, thyme, ginger, and nutmeg.
Bring to a gentle simmer and cook for 10 minutes.
Remove from heat and blend until smooth using an immersion blender.
Add additional broth if necessary to adjust the consistency.
Return to low heat and stir in the heavy cream.
Taste and adjust seasoning.
Melt butter in a small skillet over medium heat.
Add completely dry sage leaves.
Fry approximately 20–30 seconds per side, watching closely.
Transfer crispy sage to a paper towel.
Ladle soup into bowls.
Top with crispy sage and roasted pumpkin seeds.
Add a small cream swirl if desired and serve.