Preheat your oven to 400°F (200°C). Scatter pumpkin chunks and whole garlic cloves on a baking sheet, then drizzle with olive oil. Roast for about 25-30 minutes until the pumpkin is tender and slightly caramelized, and the garlic is soft and fragrant.
Remove the roasted pumpkin and garlic from the oven. Let the garlic cool slightly, then squeeze the roasted garlic out of its skins into a blender or large bowl.
Transfer the roasted pumpkin to the blender or use an immersion blender directly in the pot. Add the roasted garlic, ground cinnamon, and nutmeg.
Pour in a cup of warm vegetable broth and blend until completely smooth and creamy, about 1-2 minutes. If using a blender, do this in batches if necessary.
Pour the pureed mixture into a large pot, then add the remaining broth. Bring the soup to a gentle simmer over medium heat, stirring occasionally, for about 10 minutes to develop flavors.
Stir in the heavy cream and season with salt and pepper to taste. Continue to simmer for another 2-3 minutes until heated through and slightly thickened.
Taste and adjust seasoning, adding more salt, pepper, or spices if desired. The soup should be silky smooth with a warm, inviting aroma.
Serve the creamy pumpkin soup hot, garnished with toast or pumpkin seeds if desired, and enjoy the cozy flavors of fall.