Here is my favorite trick for getting super clean slices of desserts like this Oreo pie or frozen cheesecake: Dip a large chef’s knife in very hot water or run it under very hot water for a few seconds. Immediately wipe it dry with a clean towel. The knife will be warm enough to cleanly slice through the cold pie! Dip the knife back in the hot water for each slice, wiping it dry each time.