In a large pot melt butter. Add onions and celery, cooking for 3-5 minutes until translucent.
Add sweet potatoes, apple and stock to the pot and simmer for 10-15 minutes until sweet potatoes are soft. Allow to cool fully.
In a blender, add pumpkin puree and the cooled ingredients from your pot. Blend on low, then high speed until smooth and creamy.
If planning to eat now, return to the pot to heat, adding salt, pepper and any other desired spices. If not cooking now, store per the directions listed above in this blog post.
Topping ideas: spinach, croutons, herbs, cheese (mozzarella, parmesan, gruyere, and Swiss work well!) or herbs (cilantro, parsley or chives are great!)