Although I'm an avid baker, I'll be the first to admit, I'm a HORRIBLE cutter. When I try to cut bread or bars like this, they usually end up being uneven, all different sizes and generally, a mess. I've learned a few tricks though over the years and thought I'd share them since there might be a few of you out there who need remedial 101 cutting lesson like I do. These tips refer to any type of dessert bars.
1) Even if you will serve the bars at room temperature, refrigerate them before cutting. The cuts will be much cleaner and easier, especially if there's icing involved. Then just let the bars return to room temperature before serving.
2) Use your longest, sharpest knife to make the cuts.
3) Use hot tap water to clean your knife in between cuts. Just run it under the tap water and then dry it each time with a paper towel.
4) I use a metal ruler to make even size bars. If you have a good eye, you won't need this but I always use one. I decide how big I want the bars and make tiny little cuts along each side at the appropriate place, then just connect the cuts to slice into bars. I keep the metal ruler in a handy place in my kitchen.