In a heavy sauce pot over medium-low heat, cook the flour and butter stirring constantly until roux achieves a light caramel color.

Add the broth and brown sugar, bring to a boil, then lower to a simmer.

Stir in the sweet potatoes and spices, bring to a simmer again, and cook for 5 minutes more.

In a blender, puree the soup in batches and return to saucepot.

Add the milk and reheat soup. Season with salt and peper. Ladle into warm bowls and serve!