In a large stock pot, melt your butter, then add onions and leeks. Cook on medium-high heat until the onions are soft and brown and deliciously caramelized, about five minutes. Stir occasionally.

Add your sweet potatoes, and cook, stirring occasionally until they are cooked and soft on all sides, about five minutes.

Add the spices, broth and water, making sure that all of the vegetables are covered in liquid.

Bring to a boil, and let cook until the sweet potatoes are completely soft all the way through and easily speared with a fork, about 15-20 minutes.

Add cream and stir, cook for another 5 minutes.

Now, you have two options. If you have an immersion blender, remove the pot from the stove and carefully blend with the immersion blender until all the lumps are gone.

If you are using a regular stand blender, carefully spoon the soup in until it fills the pitcher halfway. Remove the plastic centre from the lid, and cover the hole with a folded cloth (if you don't do this, the steam from the hot liquid will make it explode off!). Keep the lid and the cloth in place with your hand while you blend the soup until it's smooth. Remove the soup and repeat until all the soup is blended.

Serve with some delicious crusty bread.