Add butternut squash, apple, pear, carrots, and leek to 6-quart or larger slow cooker. Sprinkle curry powder, cinnamon, and allspice over top. Season with salt and pepper.
Pour chicken stock over vegetables and stir to combine. Cover and cook on high for 3 hours or low for 6 hours, until vegetables are very tender.
When done, remove lid and let cool slightly (5 minutes). Puree with immersion blender until completely smooth. (Or carefully transfer in batches to a regular blender.)
Temper the cream: Add 1-2 spoonfuls of hot soup to the cream, whisk, then add tempered cream to the slow cooker. Blend again until cream is fully incorporated and soup is silky smooth.
Taste and adjust seasonings. Ladle into bowls and top with toasted pumpkin seeds and fresh parsley.