This cake was excellent! Toasting and grinding the walnuts took some effort but it was well worth it in the end. I replaced the vanilla extract with Grand Marnier since I was out, and used apricots preserves for the middle filling. Making it the day before to let the jam soak in was good advice, it turned out really moist.
I made it for a birthday, so to make more special I added a thin coat of chocolate frosting on the sides, and pressed some ground walnuts over the frosting. Then I covered the top with whipped cream and added birthday decoration. Everyone really like it! See a picture of the final cake at http://www.flickr.com/photos/sopha/4411233067/