Melt the butter and chocolate chips in a pan over low heat. Let the mixture cool slightly so that when you add the marshmallows they won't melt.
Stir in the walnuts and the marshmallows. Let cool.
Spread coconut on waxed paper. Divide the cooled mixture into two even portions. Form each portion into a long roll. Coat the rolls with the coconut, I do this by using the parchment paper to roll them back and forth as the mixture is sticky!
Wrap the rolls in waxed paper and then again in plastic wrap. Refrigerate overnight or longer.
To serve, defrost and cut into slices that are around 1/3 of an inch thick.
Notes
Nutritional values will vary due to brands of products used.