Add the chopped onions and sauté with 2 tbsp of water for 3 to 4 minutes, then add the garlic and cook a minute more.
Add the sweet potatoes, vegetable stock, red pepper , and brown rice. Increase the heat to high and bring to a boil. Reduce heat to a simmer, and simmer uncovered until the sweet potatoes can be easily pierced with a fork, about 20 minutes.
Use an immersion blender to purée the soup or work in batches and purée the soup in a standing blender.
Add the cream and milk to the soup, and heat on medium until the soup is heated through. Add salt and pepper to taste.