Combine evaporated milk, butter, sugar and marsh-mallows in 2-quart bowl.
MICROWAVE 3 to 4 MINUTES on HIGH, or until marshmallows puff and mixture begins to boil.
MICROWAVE 3 to 4 MINUTES on '6', or until mixture boils and sugar dissolves completely.
Stir in chocolate chips, nuts and vanilla.
Beat until smooth.
Spread in buttered (8 x 8-inch) baking dish.
Cut into 1-inch squares.