Considering my last name is Silbernagel, I will have to try this recipe! Thanks for posting, it sounds yummy. Might be a nice Valentine's Day dessert considering the berries.....
You could certainly use the Bavarian cream as a filling. In fact the famous Schwarzwälder Kirschtorte (Black Forest Cake) is, more-or-less, cake filled with Bavarian cream in that it uses gelatine to thicken and set the whipped cream filling. I would suggest you find any good recipe for Black Forest Cake on the Internet and adapt it to these ingredients. I would suggest using the same spring-form pan that you baked it in, to assemble the cake, layer by layer. If you like alcohol in your desserts, you could use schnapps and the juice from the fruit to moisten the cake, then spread the fruit on top and spread a generous layer of the cooled but not yet set Bavarian cream on top of the fruit. Place the next layer of cake on top and continue, ending with a layer of Bavarian cream and decorating the top with whipped cream or crème chantilly and some of the fruit. You may also thicken the whipped cream with gelatine and frost the sides of the cake with it.
Well, I have been German all my life, but I have never heard of Silbertorte :-) I even googeld it and it seems that what is meant is Bienenstich (Bee-Sting-Cake) but that is quite a different recipie. I think your friend lost part of the recipe. I am happy to post if anyone is interested. Also, Bavarian Creme is a wonderful dessert and might certainly used as a cake filling, but it is not used in Black-Forrest-Cake. The filling of a Black-Forrest-Cake consists, apart from cherry-compote, of simple whipped cream, flavoured with Kirsch and stabilised with gelatine.
Nevertheless, both recipes sound nice.
I would love the receipe for Bienenstich, as I have tried them in Germany myself.