Add the onion, garlic, pumpkin puree, tomato sauce, maple syrup, stock, cinnamon, and salt to a 6-quart slow cooker, stirring to combine.
Cover and cook on high for 4-5 hours or low for 6-8, or until the onion is very tender.
Uncover and add the cream or coconut milk and lemon juice. Using an immersion blender, blend until very smooth. Alternatively, working in batches, carefully ladle the soup into a blender and blend on high until smooth.
Add the rosemary and sage if using, stirring to combine. Taste and add additional salt if desired.
Nutrition information calculated with low sodium chicken stock, maple syrup and full-fat canned coconut milk.For Whole30 or a low sugar version, omit the maple syrup.For vegan and vegetarian, be sure to use vegetable stock.To make this recipe in the pressure cooker, see this instant pot pumpkin soup recipe.For more ingredients & modifications, see the full blog post above.