Scoop out the cookie butter as well as the frosting into a microwave-safe bowl. Microwave it for 30 seconds, remove it, and stir. Microwave the mixture for another 20 seconds, remove it and stir.
Working quickly while the mixture is still warm, pour it into your prepared pan. Push the fudge into the corners of the pan and smooth the top.
Allow the mixture to cool. You can refrigerate to quicken the process or leave it on the countertop.
When cool, cut into 1-inch squares. (I cut them small because they're so rich.) Store in an airtight container on the counter or refrigerator.