Mix powdered sugar, cocoa, coffee and 3 egg yolks with 50 ml of the chocolate milk until you get a creamy mixture. Then stir in the rest of the milk. Whip the cream until it is half stiff and fold into the mixture.
Everything in the ice machine. Shortly before the end of the preparation time (depending on the machine), add the walnuts (in the desired amount) and a shot (depending on your taste) of rum or Cointreau. Certainly works with other nuts or raisins or something similar.
A little tip, the alcohol does not set the ice properly, so maybe put something in the freezer and it will get the right consistency.
Personally, I always add a little sugar to the cream (lactose-free Schlagfix is not that sweet) before I stir it in.