5 medium beets (or enough for 2 cups pureed beets) 1 cup butter, softened 1 1/2 cups dark brown sugar 3 large eggs 1 teaspoon vanilla extract 1/2 cup cocoa powder 1 1/2 cups all - purpose flour 2 teaspoons baking soda 1 teaspoon cinnamon Pinch of salt Confectioner's sugar, for dusting (pastryaffair.com)