The colors and flavor of this moist cake are a knockout. The recipe is adapted from The Victory Garden Cookbook by Marian Morash (Knopf, New York, 1982).
Butter and lightly flour a 10-inch tube pan. Place chocolate and vanilla in a small saucepan and set, covered, in a larger pan that you’ve just filled with boiling water.
Sift together all dry ingredients and set aside. In a large bowl beat the sweet potatoes and oil together, then beat in the eggs one by one until well blended. Slowly add dry ingredients and mix well; stir in nuts. Put one-third of the mixture in another bowl and stir in the chocolate, which should be melted smooth by now. Alternate the batters in the tube pan, as you would for a marble cake. With a knife, cut through the two batters to swirl together slightly. Bake in a preheated 350° F oven for 1 to 1-¼ hours, or until the sides have shrunk away from the pan, the top is springy, and tester comes out dry. Let cool 10 minutes and then remove from the pan and cool on a rack. If desired, drizzle with a thin confectioners’ sugar glaze (beat 2 to 3 tablespoons boiling water into 1-½ cups confectioners’ sugar).