Bring a full pot of water to a boil and add the beets. Boil for about 25 – 30 minutes until beets are soft when poked with a fork. Let to cool and peel. Puree beets in a food processor until smooth. Preheat oven to 350 degrees. Melt the chocolate chips, using a double boiler or microwave. Add very hot espresso, mix with a wooden spoon or spatula. Add cubed butter and stir until smooth. Whisk together flour, sugar and cocoa powder. Whisk yolks and ad them to a chocolate mixture, mix well. Then add beet puree and flour mixture, mix one more time. Beat whites until soft peaks. Gently mix whites with a batter, stirring with a spatula just until combined. Coat a 9-inch springform pan with cooking spray. Pour the batter into the pan. Transfer into the oven, reduce heat to 325 F. Bake until a toothpick inserted into the center comes out clean, about 40 minutes. Let cool in pan on a wire rack for 15 minutes. Whip cold heavy cream with a confectioners sugar and poppy seeds. Serve warm cake with a tablespoon of whipped cream.