IDAHO CHOCOLATE CAKE

BON APPETIT

1 4-ounce russet potato, peeled
2 cups sour cream
1 3/4 cups cake flour
1 3/4 cups sugar
3/4 cup unsweetened cocoa powder (preferable Dutch process)
1/2 cup (1 stick) unsalted butter, room temperature
2 large eggs
1 1/2 teaspoons baking soda
1 teaspoon vanilla extract
1/2 teaspoon salt

Sour Cream Frosting

Position rack in center of oven and preheat to 350o F.  Butter 9 x 13-inch cake pan.  Dust with flour.

Shred potato in food processor using shredding disc.  Leave potato in food processor.  Using the food processor steel knife, add half of remaining ingredients except frosting and mix 3 minutes, stopping once to scrape down sides of work bowl.  Transfer potato mixture to large bowl; do no clean work bowl.  Add all remaining ingredients except frosting to processor and mix 3 minutes, stopping once to scrape down sides of work bowl.

Add contents of work bowl to potato mixture.  Stir to combine.  Transfer to prepared pan.  Bake until tester inserted in center comes out clean, 35 to 40 minutes.  Cool completely in pan on rack.  Invert onto platter.  Spread frosting over top and sides of cake.

SOUR CREAM FROSTING

3 cups powdered sugar
1/4 cup (1/2 stick) unsalted butter, room temperature
3 tablespoons sour cream
1 tablespoon vanilla extract

Using food processor with steel knife, blend all ingredients until smooth, about 2 minutes, stopping once to scrape down sides of bowl.