Last week, a customer begged me to make a dozen Napolean slices for him. I hate making them because the slicing is so messy. Basically you have three layers of baked puff sandwiched between two layers of pastry cream. You can freeze only so long but you still have to slice, and when you slice, you inadvertently push down, squishing the cream out. I've done electric knives, freezing, but it always ends up as a mess.
What I came up with was a frame to put the block of unsliced Napoleons in. This device greatly resembles a woodworker's "miter box" a very simple frame made to guide the saw to make 90 or 45 degree cuts.
I made mine with slits every inch and half to guide my knife. The frame holds the pastry block tight, so it doesn't move around, and since it doesn't move around, I don't need to push down, but can go hog wild "sawing" back and forth with no worries about disturbing the whole block. See the below pic