Whip the cream till soft peaks form .
Blend the vanilla crumbs in a mixer to get even sized crumbs .
Similarly make chocolate crumbs .
In a mixing bowl , mix chocolate crumbs and ganache and make a semi soft dough .
In another bowl add vanilla crumbs and whipped cream and mix well to get a smooth semi soft dough .
Place the chocolate dough between two parchment sheets and roll into a thick rectangle .
Similarly roll the vanilla dough .
Place the vanilla rectangle over the chocolate one .
Now starting from the long side start rolling the rectangles into a log .
Make sure the log has a smooth surface .
Wrap it in a cling film and place it in the refrigerator till firm , preferably overnight .
Remove the film and cut into slices of your choice .