In a large pot or stockpot, add the oil and butter and saute the onions, on high heat, until tender.
Add the minced garlic and cook another minute.
Add the pumpkin puree, chicken stock, brown sugar, salt and spices. Stir to make sure all ingredients are blended well.
Cover pot and simmer for about 20-25 minutes.
Blend the soup using an immersion blender or in batches in a regular blender. *** If you use the blender, let the soup cool a little bit first. Then remove the plastic part in the middle of the lid for the blender. Cover the top with a towel, then blend.
Return the mixture to the pot and add the heavy cream.
Cook for 5-10 minutes.
Garnish the soup with toasted pumpkin seeds, croutons and/or a drizzle of heavy cream.