In a 2-quart glass bowl, combine peanut butter, chocolate chips, marshmallows, cream and vanilla. Place in a microwave oven and heat on HIgh 1 1/2 to 2 minutes, or until marshmallows are melted and mixture is smooth when stirred. Turn into a foil-lined 8-inch square baking pan. Let cool 1/2 hour, then refrigerate until firm. Cut into 1-inch squares.