Preheat oven to 200°C (400°F)
Peel, deseed, and cut pumpkin into chunks
Place pumpkin on a baking tray, drizzle with olive oil, and season with salt and pepper
Roast for 30–40 minutes, or until fork-tender and lightly caramelized
Heat oil in a pot and sauté chopped onion until soft
Add garlic and cook for about one minute
Add roasted pumpkin along with cinnamon and nutmeg
Pour in vegetable broth and simmer for 10–15 minutes
Allow the soup to cool slightly before blending, or blend in batches to avoid splashing
Stir in cream if using and add lemon juice or vinegar
Adjust seasoning and serve hot