Crumble the biscuits into small pieces. Set aside a part of them, blend the other part with a blender.
Add the sour cream, rum and chopped walnuts to the blended part.
Knead until homogeneous.
Form the dough into a roll. Melt the chocolate in a water bath. Pour it over the roll. Sprinkle generously with coconut flakes and decorate with chocolate bonbons and the remaining biscuit pieces.