Heat milk and margarine in a saucepan until melted. Remove from heat.
Stir in icing sugar and cocoa. Place over low heat and heat for another minute or two.
Stir in nuts.
Notes
A delicious rich variation is to put a layer of caramel and whipped cream in the middle. Mix 1/2 a tin of caramel with a Paddle Scraper to make it soft for spreading.