In a large bowl combine Zsweet® and margarine and beat until creamy. Add egg substitute and egg whites in 4 equal parts beating well after each addition.
Add melted chocolate, beet puree, buttermilk, and vanilla. Add the flour, baking soda, and salt (that have been previously sifted together). Beat until smooth.
Coat a 9-inch pan with cooking spray. Pour the batter into the greased pan and bake for 40 minutes or until a toothpick comes out clean.
For the icing, use a spice mill and grind Zsweet® until powdery. Blend with cocoa powder. Add to cream cheese and blend until smooth. Add vanilla and beat until fluffy. Ice the cake when it has completely cooled.