Roughly chop the nuts. Melt the marshmallows and butter in a saucepan over low heat while stirring. Stir in the nuts and popcorn quickly with a wooden spoon (the mixture sticks and is very sticky). Remove from the heat.
From the mass immediately and quickly with greased hands (be careful: mass is warm and very sticky) form 14 snowballs, greasing hands again and again. Place snowballs on a baking tray covered with baking paper. Let it cool down for about 1 1⁄2 hours. Dust with icing sugar.