In a large bowl, cut the chocolate chips into the butter; set aside.
In a medium saucepan, over medium heat, bring the sugar, milk and 20 marshmallows to a boil; boil for five minutes, stirring constantly.
Pour this mixture over the butter and chocolate chips; stir until thick.
And nuts, vanilla, and frozen marshmallows.
Pour into a buttered 9 x13-inch pan.
Chill until firm.
Cut into squares when chilled.