Cut the plums in half and soak in port wine for about 1 hour. Put the plums in a sieve, collect the port wine and use it for other purposes. Dab plums well dry.
Form marzipan into approx. 30 balls, press flat. Wrap plums in it and roll them smooth between the palms of your hands. Dust about half of the pralines with icing sugar, roll the remaining pralines in cocoa.