To make sweet potato bisque, roast sweet potatoes in an oven for 30 minutes, and allow them to cool. Sauté garlic and onions in butter and olive oil before adding potatoes, flour, sweet potatoes, broth and water. Simmer the ingredients for 30 minutes, and remove them from heat to puree them with a handheld blender. Reheat the soup over low heat, and add seasoning.
Gather 3 sweet potatoes, 2 cloves of garlic, 1 large onion, 4 peeled potatoes and 1 1/2 tablespoons of all-purpose flour. In addition, gather 1 tablespoon of olive oil, 1 tablespoon of butter, 1/4 cup of chicken broth, water and buttermilk. Herbs and spices for this dish include pepper, salt, ground cumin, dried thyme, ginger and nutmeg. This recipe requires 1 1/2 hours to prepare and makes 8 servings.
Roast the sweet potatoes in an oven at 450 degrees Fahrenheit for 30 minutes. Remove the sweet potatoes from the oven, and slice them open to cool while you prepare the soup. Sauté the garlic and onions in olive oil and butter until they are slightly brown and soft. Add potatoes, and sauté the ingredients for one minute. Stir in the flour, and add the broth, water and sweet potatoes. Bring the mixture to a boil, and reduce the heat to medium-low. Simmer for 30 minutes until the vegetables are tender.
Remove the ingredients from heat, and puree the vegetables into a soup with a handheld blender. Return the soup to the pot, and reheat it over low heat. Add the seasoning, and stir well.