Heat olive oil in a skillet over medium heat, then add the finely chopped onion. Sauté until translucent and fragrant, about 5 minutes, until the onions are soft and slightly golden.
Add the minced garlic to the skillet and cook for another 1 minute, until it releases a fragrant aroma without browning.
Transfer the sautéed onions and garlic into your slow cooker, then stir in the roasted pumpkin puree, tomato paste, apple cider, cinnamon, smoked paprika, and nutmeg. Mix well to incorporate all the flavors.
Cover and cook on low for about 6 hours, allowing the flavors to meld and the soup to warm through, filling your house with a cozy aroma.
Once cooked, carefully blend the soup directly in the slow cooker using an immersion blender, or transfer to a blender in batches. Blend until smooth and velvety, with a consistent, creamy texture.
Taste the soup and season with salt and freshly ground black pepper as needed. If you prefer a richer finish, stir in the heavy cream now for extra creaminess.
Pour the hot, smooth pumpkin soup into bowls, garnish with a swirl of cream or a sprinkle of smoked paprika if desired, and serve immediately.