I made sweet potato soup last night and just had a taste test with it this morning. Its thick and very smooth while cold and very strong on the sweet potato flavor. When hot, the ginger and orange flavors come through more. I liked it hot better.

10 tablespoons (1 1/4 sticks) butter
3 1/2 pounds red-skinned sweet potatoes (yams), peeled, cut into 1/2-inch pieces
1 tablespoon golden brown sugar
1 small yellow onion, minced
3 teaspoons ground ginger
salt and pepper to taste
2 large shallots, chopped
1 1/3 cups finely chopped celery
4-5 cups homemade chicken broth (mine had a bit of curry in it)
1 1/3 cups orange juice

Preheat oven to 400°F. Melt 4 tablespoons butter in large roasting pan. Remove from heat. Add sweet potatoes and sugar and toss to coat. add minced onions, ginger, salt and pepper. Roast until very tender and starting to brown, stirring occasionally, about 30 minutes.
Melt 4 tablespoons butter in pot over medium heat. Add shallots, celery and remaining 1 1/2 teaspoons ginger and sauté until shallots begin to soften, about 5 minutes. Add roasted sweet potatoes and sauté 2 minutes. Add broth and orange juice until vegetables are just covered. Bring mixture to boil. Reduce heat and simmer until shallots and celery are very tender, about 20 minutes.
Working in batches, puree soup in processor. Return soup to pot. Thin with more broth, if desired. Season with salt and pepper.

The recipe I found used leeks instead of shallots and had an orange creme fraiche with hunks of lobster tails in the soup.

Enjoy,
Seth