1. Lightly spray a paper towel with nonstick cooking spray and use it to rub the bottom and sides of an 8-inch square baking pan.

2. Put the cereal in a large bowl and set aside.

3. Pour 1/4 cup water into a small saucepan. Gently add the sugar and corn syrup (do not let any sugar or syrup get on the sides of the pan) and use a small wooden spoon to stir the mixture until just combined.

4. Put a candy thermometer in the saucepan. Cook over medium-high heat and bring to a boil; cook until the mixture reaches the soft ball stage, 235 degrees F.

5. Remove from the heat, stir in the butter, and pour the mixture over the cereal. Working quickly, stir until the cereal is thoroughly coated, then pour it into the prepared pan. Using your hands, press the mixture into the bottom of the pan (do not press up the sides). Let the crust cool to room temperature while you make the next layer.

6. In a large nonreactive metal bowl, stir together the chocolate and the peanut butter. Set the bowl over a saucepan of simmering water and cook, stirring with a rubber spatula, until the mixture is smooth. Remove the bowl from the pan and stir for about 30 seconds to cool slightly. Pour the mixture over the cooled crust. Put the pan in the refrigerator for 1 hour, or until the top layer hardens.

7. In a large nonreactive metal bowl, combine the chocolate, corn syrup, and butter. Set the bowl over a saucepan of simmering water and cook, stirring with a rubber spatula, until the mixture is completely smooth. Remove the bowl from the pan and stir for 30 seconds to cool slightly. Pour the mixture over the chilled milk chocolate peanut butter layer and spread smoothly into an even layer. Put the pan into the refrigerator for 1 hour, or until the topping hardens.

8. Cut into 9 squares and serve. The bars can be stored in the refrigerator, covered tightly, for up to 4 days.