In a 3 quart microwave safe bowl place the chocolate chips, peanut butter, and butter. Place on 50% power for 4 to 5 1/2 minutes; stirring after 3 minutes.
Check after 4 to 4 1/2 minutes to see if the mixture is completely melted and completely smooth.
It needs to be melted and smooth enough for the marshmallows and nuts to be added.
Do NOT over cook as the mixture will taste burnt.
Once it is completely melted and smooth enough, add the marshmallows and nuts.
Fold in the marshmallows and nuts gently. You do not want the marshmallows to melt.
Once that is complete, spread the mixture in a lined (or greased/buttered) 10x13 pan and refrigerate overnight.
(This freezes well!)