1. Heat oven to 375°F. Line 15-1/2 x 10-1/2 x 1-inch jelly-roll pan with heavy-duty foil. Generously spray foil with nonstick cooking spray. Arrange crackers in bottom of pan with edges touching; set aside. Cut each peanut butter cup in half; set aside.
2. Heat butter and brown sugar over medium heat in heavy medium saucepan, stirring frequently, until butter melts. Increase heat to high; boil without stirring until entire surface is covered with bubbles (about 3 minutes). Pour mixture over crackers, spreading evenly to cover crackers.
3. Bake 5 minutes; remove from oven. Cool 3 minutes. Sprinkle peanut butter chips evenly over crackers. Cool an additional 2 minutes; sprinkle milk chocolate chips evenly over surface. Let stand 5 minutes or until chips have softened; spread evenly over crackers. Sprinkle peanut butter cup halves and peanut halves over chocolate mixture, pressing in lightly. Allow to sit until chocolate is set up and firm. Break or cut into pieces. Store covered in a cool, dry place. About 40 cracker squares.
Note: Toffee portion continues to firm for two days. Cracker squares can be kept for at least two weeks.