Stir marzipan paste, Grand Marnier and ground pistachios until smooth. Fill into a piping bag with perforated spout and squirt into the hollow balls. Melt the dark chocolate coating in a hot water bath, fill into a freezer bag, cut off a small corner and spray the ball openings with it.
Smooth with a knife and let it set. Place the balls on a cake rack with the round side facing upwards. Melt the white couverture in a hot water bath, fill it into a freezer bag, cut off a small corner and decorate the balls in drops.
Halve the pistachios lengthwise and place one half on each praline. Results in about 63 pieces.