Nonstick pan spray
1 3/4 cups all-purpose flour, plus more for the pan
1 1/2 cups granulated sugar
1 cup unsweetened Dutch-processed cocoa powder
1 tsp. baking powder
1 tsp. baking soda
1/2 tsp. fine sea salt
1 1/4 cups low-fat buttermilk
1 cup plain nonfat Greek-style yogurt
4 egg whites from large eggs
1 tbsp. extra virgin olive oil
2/3 cup loosely packed, finely grated beets
8 oz. reduced-fat cream cheese
1/4 cup unsalted butter, softened
2 cups powdered sugar
6 tbsp. unsweetened Dutch-processed cocoa powder
1/2 tsp. pure vanilla
2 tsp. nonfat milk
For cake: Preheat oven to 350 degrees. Coat a 10-inch round cake pan with pan spray and coat it lightly with flour; knocking out excess.
Whisk together flour, sugar, cocoa powder, baking powder, baking soda and salt. In a large bowl, whisk buttermilk, yogurt, egg whites and oil until smooth. Stir in beets, then flour mixture, just until incorporated. Transfer batter to prepared pan and bake for 40 minutes or until cake is slightly domed out and a toothpick inserted near the center comes out clean. Cool pan on a rack for 20 minutes. Then run a knife around the edge and invert cake directly onto rack. Cool completely.
For frosting: Using an electric mixer, beat cream cheese and butter on medium speed for 1 minute, until smooth. Sift in powdered sugar and cocoa powder and mix, starting on low and increasing to medium speed as the sugar is incorporated, until frosting is completely smooth. Add vanilla and milk on low speed, mixing until incorporated.
To serve: Frost the top of the cake first, starting at the center and pushing the frosting out to the sides. Frost sides. Any leftover cake may be kept, covered and refrigerated, for up to 2 days.