How to Make It
Prepare the Crust: Preheat oven to 350°F. Place Trefoils cookies in a food processor; process until finely ground, about 10 seconds. Add powdered sugar and melted butter; pulse 10 times or until well blended. Press evenly into bottom of a 9-inch square baking pan. Bake in preheated oven 10 minutes. Remove from oven.
Prepare the Brownie Layer: Arrange Samoas evenly over warm crust. Prepare brownie mix according to package directions, and pour batter evenly over Samoas. Bake in preheated oven until top is crackly, but not fully cooked, 18 to 20 minutes. Remove from oven.
Prepare the Cheesecake Layer: Arrange Do-si-dos evenly over warm brownie layer. Beat together cream cheese, condensed milk, vanilla, and egg in a bowl with an electric mixer on medium speed until smooth, about 1 minute. Pour cheesecake batter over Do-si-dos, spreading evenly with an offset spatula. Bake in preheated oven until edges begin to turn golden brown, but center is still undercooked, about 10 minutes. Remove from oven.
Prepare the Peanut Butter Blondie Layer: Arrange Tagalongs evenly over warm cheesecake layer. Beat together brown sugar, butter, and peanut butter in a bowl with an electric mixer on medium speed until smooth, about 1 minute. Beat in egg and vanilla until blended. Gradually add flour, beating on low speed just until combined. Dollop batter evenly over Tagalongs; gently spread batter using your hands or a greased spatula. Bake in preheated oven until blondie mixture is golden brown and set, 20 to 25 minutes.
Remove from oven, and top with 4 of each type of cookie. Return to oven, and bake 5 minutes. Cool in pan on a wire rack, about 1 hour. Drizzle top with melted chocolate, and chill 1 hour before serving. Slice with a sharp knife. Bars will be very thick, so handle carefully!