Preheat oven to 400°F (200°C). Toss cubed sweet potatoes with 1 tbsp olive oil, salt, and pepper. Roast for 20-25 minutes, or until tender.

While sweet potatoes are roasting, sauté onion and garlic in a large pot over medium heat until softened. About 5 minutes.

Add roasted sweet potatoes and vegetable broth to the pot. Bring to a boil, then reduce heat and simmer for 10 minutes.

Carefully transfer the soup to a blender (or use an immersion blender) and blend until smooth and creamy.

Return the soup to the pot and stir in heavy cream, cinnamon, and nutmeg. Heat through, but do not boil.

Season with salt and pepper to taste. Serve hot.