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1
Position a rack in the lower third of the oven and preheat the oven to 350u00b0 F. Grease a 9- by 13-inch glass baking dish with vegetable oil spray or butter.
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2
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.
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3
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.
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4
Bake for 30 minutes at 350u00b0 F, then reduce the heat to 325u00b0 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.
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5
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.
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6
This cake keeps, covered, in the refrigerator for up to 5 days.
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7
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 350u00b0 F and 20 minutes at 325u00b0 F. Fill and frost the cake with 1 1/2 batches of the Cream Cheese Frosting.
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8
Warm the cream cheese and butter in a microwave oven on low until soft but not melted.
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9
Add the confectioners' sugar and vanilla and beat with a spoon until smooth.
