A half-lap joint is good-looking, functional and, once you get good at it, quick to cut with hand tools. But even if you get the joint to fit snugly, the intersections may show ugly gaps due to slight imperfections in your sawing or chiseling technique.
Traditional Japanese woodworking has a method to completely erase those gaps, and to get the joint fitting so tightly that when removed, you can actually see the imprint of one workpiece on the other:
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The technique is called kigoroshi, and here's how they do it. (Sorry folks, the creator has disabled embedding.)
The Ultimate Wood Joint Visual Reference Guide