Preheat oven to 350°F (175°C). Grease a 10 cup Bundt pan with baking spray containing flour.

Sift together flour, cocoa powder, baking soda, baking powder, and salt into a bowl.

Separate eggs, and whip egg whites to stiff peaks. Set aside.

Cream together brown sugar, white sugar, butter, and oil for 2-3 minutes. Add egg yolks, beat for 3 more minutes, then mix in beet puree and vanilla. Alternate adding sifted flour mixture and buttermilk until just combined. Fold in chocolate chips.

Gently fold whipped egg whites into the batter in two additions, until no streaks remain. Pour batter into prepared pan and smooth the top evenly.

Bake at 350°F until the cake springs back lightly when touched or until a skewer inserted comes out with moist crumbs, 50-55 minutes.

Cool cake in the pan for 20 minutes, then loosen edges with a knife and invert onto a wire rack. Cool completely.

Combine powdered sugar, heavy cream, beet puree, vanilla, and salt in a bowl. Mix until smooth. Adjust consistency as needed by adding cream or powdered sugar.