Divide dark chocolate into pieces and melt in a hot water bath. Leave to cool a little. Sieve the icing sugar onto the work surface and knead with the marzipan paste. Form into a roll, cut into about 16 equally sized pieces and shape into oval acorns.
Put the chocolate sprinkles in a small bowl. Dip acorns with the blunt end first in chocolate, then turn them over in crumbles. Let dry on a cake rack.