Above, the mortices were cut with a router and the tenon is a loose piece of hardwood machined to be a comfortable sliding fit. Note the grain direction on the tenon. The cross grain will resist splitting across the joint.
It all went together well and is held by four blocks, which are clamped to the work while another clamp on each face provides compression between the blocks. This provided enough pressure to close the joint and squeeze out enough thickened glue to satisfy me that the joints were fully wet. I used epoxy for this one, applied thin- especially in plenty around all that end-grain, allowing it to soak in before applying thickened stuff liberally.