Beat the butter with the sugar and egg until frothy, then fold the nuts mixed with flour and baking powder into the foam mixture. Put the dough on a greased and floured deep baking sheet. Bake at 200 degrees for about 20 minutes.
For the filling, beat the cream with the cream stabilizer. Put in the jar of jam. Spread the mixture on the cooled cake.
Brush the shortbread biscuits with a little wine or apple juice (so that they become soft and sliceable). Then spread the biscuits on the cake. Finally sprinkle the whole thing with a thin layer of cocoa (preferably through a hair sieve), or cover with a chocolate icing.