Measure the cereal into a large mixing bowl and set aside. Melt the marshmallows and butter together in a medium saucepan over medium heat (or in the microwave for about 3 minutes, but keep watch so the marshmallows don’t puff over the sides of the bowl!). Pour the melted marshmallow mixture over the cereal and mix well so the cereal is coated. Pour into the prepared pan and use a buttered piece of wax paper to press evenly into pan.
In the microwave, melt the peanut butter until thin, about 1 minute. Gently stir in the quartered peanut butter cups and then pour over the treats. Using the back of a spoon, gently spread the peanut butter mixture evenly across the top.
Again in the microwave, melt the chocolate chips. Using a spoon, drizzle the melted chocolate across the top. Place the pan in the refrigerator to set before cutting and serving. Store in an airtight container.