Finely grind the pistachio nuts in the food processor. Sieve powdered sugar. Knead the ground pistachios with rum, marzipan and powdered sugar until smooth and form small balls. Press one half of the nut onto each pellet.

Heat the chocolate in a water bath over a mild heat and let it cool down. Heat again over low heat and submerge the balls halfway. Place on baking paper and let dry slowly at room temperature.