For the walnut pralines, knead the marzipan with powdered sugar, rum and chopped nuts. Roll out the mixture on a sugar-dusted work surface to a thickness of approx. 1 cm and cut out discs (3 cm in diameter).
Melt the white chocolate with margarine in a water bath, stir until smooth and dip the marzipan slices in it.
Immediately cover the walnut pralines with half the walnuts. Store in a cool place.