Heat the large pot over medium heat and add the olive oil. Once shimmering, add the chopped onion and sauté until translucent and fragrant, about 5 minutes.
Add the pumpkin puree to the pot, stirring to combine with the onions. Cook for another 2 minutes to deepen the flavors.
Pour in the vegetable broth, stirring well to incorporate all ingredients. Increase the heat slightly to bring the mixture to a gentle simmer.
Allow the soup to simmer uncovered for about 15 minutes, stirring occasionally. The flavors will meld, and the soup will thicken slightly.
Add the ground cinnamon, a pinch of ground cardamom, salt, and pepper to the pot, stirring to evenly distribute the spices. Smell for that aromatic floral note of the cardamom.
Pour in the heavy cream and stir to create a rich, velvety consistency. Let the soup simmer for another 5 minutes to warm through and meld all flavors.
Use an immersion blender to carefully blend the soup until smooth and creamy, or transfer in batches to a regular blender, blending until silky and returning to the pot.
Taste and adjust seasoning with more salt or pepper if needed, then reheat gently if it has cooled slightly.
Serve the soup hot, garnished with a drizzle of cream or a sprinkle of herbs if desired, revealing a vibrant orange color and smooth, velvety texture.