Line an 8-in. square dish with aluminum foil; coat with cooking spray. Place half of the broken cookies in pan. , In a heavy saucepan, combine the milk, butter and chips; cook and stir over low heat until chips are melted. Remove from heat; stir in vanilla. , Pour over cookies in pan. Sprinkle with remaining cookies and peppermint candies if desired. Cover and refrigerate for at least 1 hour. Cut into squares.