Place the stock, water, sweet potato, carrots, onions, and garlic in a pot over medium-high heat. Bring everything to a boil.
Once the stock is boiling, reduce the heat to medium, and simmer the vegetables until they are tender. This usually takes me about 15-20 minutes.
When the vegetables are tender, turn off the heat. Blend the stock and vegetables with an immersion blender. Alternatively, mix the ingredients with a conventional blender in batches.
Return the soup in to the pot and stir in the spices and milk. Reheat the soup if you find the soup too cool.
Enjoy!