For the Roll
Preheat oven to 450 degrees. Prepare a 17 inch x 12 inch jelly roll pan. Grease, line bottom with parchment, and then grease and flour again. In a small bowl whisk together the cake flour and cornstarch. Separate 2 of the eggs, placing the yolks in one large mixing bowl and the whites in another. To the yolks, add the additional yolk, the two remaining eggs, and 1/2 cup sugar. Beat on high speed for five minutes, or until thick, fluffy, and triple in volume. Beat in the vanilla.
Sift half the flour mixture over the egg mixture and fold it in gently but rapidly with a large whisk or rubber spatula until the flour has disappeared. Repeat with the remaining flour mixture.Beat the egg whites until foamy, add the cream of tartar, and beat until soft peaks form when the beater is raised. Beat in the remaining one tablespoon sugar and beat until stiff peaks form when the beater is raised slowly. Fold the whites into the batter and pour into the prepared pan, using an angled metal spatula to level it.
Bake for 7 minutes or until golden brown, a cake tester comes out clean, and the cake is springy to the touch.
Loosen the edges with a small metal spatula or sharp knife and, lifting by a long edge of the parchment overhang, gently slide the cake from the pan onto a flat surface. Sprinkle roll lightly with powdered sugar and roll it up while still hot. (Flip the biscuit onto a clean dish towel, carefully remove the parchment, and roll it up tightly, towel and all.) Cool on a rack. When ready to fill, unroll the biscuit.
For The Cream Cheese Filling
Finely chop chocolate in processor. Set aside.
Mix sugar and egg yolks in processor 30 seconds. Add vanilla and process until pale yellow, about 1 minute. Add cheese in batches and blend until smooth. Transfer to medium bowl. Cover and chill 1 hour. Beat whipping cream until stiff. Fold into cream cheese mixture. Cover and refrigerate until well chilled, about 1 hour. (Can be prepared 2 days ahead.)
Unroll the roll. Brush with espresso mixture. Spread a thick layer of cream cheese mixture over the roll. Sprinkle with chopped chocolate. Roll back up. Spread remaining cream cheese mixture to coat the "log". (It won't be super firm yet). Chill for one hour. Slide a fork all over log (so it will look bark-like). Sprinkle with chopped chocolate. Garnish with marzipan ornaments, meringue mushrooms, and fresh cut rosemary (optional).