In either case, it should be quite thin and very even. Allow the baked mixture to cool slightly, then spread the chocolate thinly over the top. Cut into bars while warm.
Timing is everything when spreading the chocolate and cutting the bars.
The baked mixture needs to have cooled enough to be firm while the chocolate is spread, but not so cool as to be brittle when the bars are cut. The bars generally have to be cut a second time after they've been refrigerated. May be sprinkled with chopped nuts while chocolate is sticky. From a recipe book issued by the Nestle Company c. l950. They used white flour, naturally, but otherwise I have meddled very little.