Sweet Potato-Chocolate Nut Cake

We have found many creative ways to use sweet potatoes over the years.  This is our favorite dessert so far.  It's from Marian Morash's The Victory Garden Cookbook.  

Sweet Potato Chocolate Nut Cake

1 1/2 pounds sweet potatoes, peeled,
    cooked and pureed to equal 2 cups 
1 1/2 cups vegetable oil 
4 eggs 
1 teaspoon vanilla extract
3 cups all-purpose flour 
1 1/2 cups granulated sugar 
2 teaspoons baking powder 
2 teaspoons baking soda 
2 teaspoons cinnamon 
1/2 teaspoon ginger 
1/4 teaspoon cloves 
1/4 teaspoon nutmeg 
1 teaspoon salt 
1 cup chopped nuts 
1/4 cup melted chocolate

Blend together potatoes, oil, eggs and vanilla extract. Add slowly the dry ingredients that have been mixed together. Fold in the nuts.  Separate 1/3 of the batter and stir in chocolate. Pour the plain batter in a greased 9 x 13-inch pan and swirl chocolate batter in to give it a marbleized effect. Bake at 350 degrees for 1 hour or until the sides have shrunk away from the pan, the top is springy, and tester comes out dry.  Let cool 10 minutes, then remove from pan and cool on rack. 

(Makes a 10-inch tube cake)