Where the legs meet the shoulder there is a detail feature that goes into a pocket on both sides of each leg.
This pocket is easier to cut out before the layers of the leg are assembled. To make these cuts I used a router with a guide collar and a template. I stared out by making a template out of a piece of scrap 1/4” MDF. The cut out on the right is the actual template.
The shape is pretty simple so I just laid it out based on the measurements in the plans being sure to add the distance between the edge of the guide collar and the edge of the bit to the measurements so that the template cutout is slightly larger then the final size of the pocket. Since the shape has some tight corners I used the smallest possible router bit, but it will still require some manual cleanup in the corners.
With the legs temporarily assembled I marked the location of the pockets. These lines will be used to align the template.
Next I screwed the template to the inside surface of one of the leg side pieces. The cut does not go all the way through this piece so I adjusted the router for the correct depth and then made the cut.
The center layer is cut the same way, but I put a scrap piece of wood under the leg piece because this cut needs to be all the way through.
With the legs again temporarily re-assembled you can see the finished pocket.