Prepare a 9-by-9-inch pan by lining it with aluminum foil, spray with cooking spray; set aside. In a large microwave-safe bowl, combine the marshmallows and butter and heat on high power to melt, about 90 seconds. Keep a watchful eye because the marshmallows will grow and swell to the top of the bowl. Immediately upon removing the bowl from the microwave, stir vigorously for about 10 seconds to combine the butter and marshmallows. Add the Malibu and stir to combine. Add the cereal, one cup at a time, and toss to coat. (I wanted to keep these gooey so I suggest not more than 6 cups of cereal, possibly only 5. I used about 5 1/2 cups) Pour mixture into prepared pan and lightly pack it down and smooth it with a spatula; set aside.
In a small microwave-safe bowl, melt the white chocolate on high power, about 45 seconds. Stop to stir and heat in 10-second bursts until chocolate can be stirred smooth, taking care not to scorch the chocolate, noting that white chocolate scorches very easily. Drizzle the melted chocolate over the bars with a spoon. Garish with sprinkles before chocolate sets. Place pan in the freezer for about 1 hour or until bars have set up before slicing and serving. Because of the alcohol in the Malibu, these will take a bit longer to set than traditional Krispy Treats to set up. Store bars in an airtight container at room temperature or in the refrigerator for up to 1 week, or in the freezer for up to 3 months. I prefer them chilled and store them in the freezer