Rice and oat flours give this moist and otherwise classic American cake a surprising delicacy while letting the spices shine through. Cool the cake thoroughly and make sure the frosting is soft before assembling.
Position a rack in the lower third of the oven and preheat the oven to 350° F. Grease a 9- by 13-inch glass baking dish with vegetable oil spray or butter.
Combine the oil, sugar, and eggs in the bowl of a stand mixer and beat on medium speed with the paddle attachment until lighter in color, about 2 minutes. Or beat with a handheld mixer on medium-high for 3 to 4 minutes.
Add the rice and oat flours, baking soda, baking powder, cinnamon, nutmeg, cloves, salt, sweet potatoes, and walnuts and beat on low speed until smooth. Scrape the batter into the prepared dish.
Bake for 30 minutes at 350° F, then reduce the heat to 325° F and bake for 30 minutes longer, or until a toothpick inserted in the center comes out clean. Set the pan on a rack to cool for at least 2 hours before frosting.
To frost, use a spoon or drop dollops of frosting all over the cake, ten spread with a small spatula. Cut into 3-inch squares to serve.
This cake keeps, covered, in the refrigerator for up to 5 days.
Note: To make this into a layer cake, grease the sides of two 9- by 2-inch round cake pans and line the bottoms with parchment paper. Divide the batter evenly between the pans. Bake for 30 minutes at 350° F and 20 minutes at 325° F. Fill and frost the cake with 1 1/2 batches of the Cream Cheese Frosting.
For the cream cheese frosting:
Warm the cream cheese and butter in a microwave oven on low until soft but not melted.
Add the confectioners' sugar and vanilla and beat with a spoon until smooth.
My career was sparked by a single bite of a chocolate truffle, made by my Paris landlady in 1972. I returned home to open this country’s first chocolate bakery and dessert shop, Cocolat, and I am often “blamed” for introducing chocolate truffles to America. Today I am the James Beard Foundation and IACP award-winning author of ten cookbooks, teach a chocolate dessert class on Craftsy.com, and work with some of the world’s best chocolate companies. In 2018, I won the IACP Award for Best Food-Focused Column (this one!).