In a 2 litre glass bowl, combine peanut butter, chocolate chips, marshmallows, cream and vanilla. Place in a microwave oven and heat on HIgh 1.5 to 2 minutes, or until marshmallows are melted and mixture is smooth when stirred. Turn into a foil-lined 20 cm square baking pan. Let cool half hour, then refrigerate until firm. Cut into 3 cm squares.