Preheat oven to 375 degrees F (190 degrees C). Bake sweet potatoes until soft, about 45 minutes. Remove potatoes, and set aside until cool enough to handle. Then peel, and place in a large bowl. With a large fork or potato masher, mash potatoes for 15 to 20 seconds (they do not need to be mashed smooth).
Spoon the potatoes into a large saucepan over medium-high heat. Stir in butter, water, tomato sauce, and half-and-half. Season with salt, pepper, and thyme. Stir in cashews, and mix well. Bring to a boil, reduce heat to medium low, and simmer until cashews are soft, about 50 to 60 minutes.
