My recipe calls for 1/2 square of baking chocolate per cookie. But trying to cut thru the bar into the indicated squares just crumble and are not neat or exact. Is there a method of somehow either warming the chocolate or softening it, so that it will cut easily/nicely from the solid bar?
You can score and snap. You make a shallow score in the chocolate using a knife or other sharp object (gentle!). Then you snap it. It works better on harder chocolates. Since all I have around the house this instant is a leftover halloween candy, I'll show the sequence here, but with this soft chocolate it would be easier to actually cut it through...
2) Pinch it. Here I pinched it between a plate and a cutting board. You may be better off using a cutting board and your fingers -- so long as your hold it down stiffly with your fingers.
3) Strike it with a blunt object. Or depending on the chocolate you can often just bend it with your fingers until it breaks.
(This basic approach is used in industry to make straight cuts in glass, tile, and silicon chips! The harder the object, the better it works. You can also try this on brittle candy, etc.)
Although the other answer is pretty genius (pretty much how you would cut bathroom tiles) it does seem a little labour intensive or over the top for the sake of cutting chocolate.
How I would personally do it at work is.
Heat large knife, either over stovetop or using a blowtorch.
Repeat as necessary when knife gets cold, giving the knife a wipe beforehand so as not to have burnt chocolate stuck to your knife.
The above method also works great for cutting jelly and cheesecake when you want a nice smooth cut.