2. In a mixing bowl, whisk the eggs and sugar together and warm the mixture over the simmering water. Whisk constantly until the mixture is warm to the touch. Remove the bowl from the heat and beat with an electric mixer on high speed until the mixture has doubled in volume, about 7 minutes.
3. With a rubber spatula, gently fold in the cake flour. Do not overmix. Pour the batter into the prepared pan and spread the batter evenly into the corners.
4. Bake the cake until it is golden brown and springs back when touched lightly, about 5 to 7 minutes. Sprinkle the top of the cake with granulated sugar and cover it with parchment paper. Place a cake rack over the cake, invert, remove the baking sheet and parchment paper and allow the cake to cool.
5. To make the syrup: Combine the sugar and water in a small saucepan and bring to a boil. Remove from heat and add the rum. (This can be made in advance and stored at room temperature for a week or more.)
6. To make the filling: Combine the raspberry jam and Cassis or water in a small bowl. (This can be made in advance and stored in the refrigerator for a week or more.)
7. To assemble the cake: Place the cake right side up on a work surface. Brush the syrup over the cake and let it soak in. Spread the jam filling over the cake, covering all but the last inch on the other side. Starting with one of the long sides, roll the cake up tightly, removing the parchment as you go. Place the cake on a baking sheet, tent with foil and refrigerate for 1 hour.
8. To make the chocolate glaze: Put the chocolate and corn syrup in a small bowl. Bring the milk to a boil in a small saucepan. Pour the hot milk into the bowl and gently stir until the chocolate is melted and the mixture is smooth.
9. Place the chilled cake on a wire rack set over a baking sheet. Pour the warm glaze over the cake to coat it completely. Tent with foil (being careful not to touch the chocolate glaze) and refrigerate for up to 24 hours.
10. To decorate: Dust the cake with powdered sugar. Place the cake on a large platter and garnish with winter greens and small fruits.