This is a domino joint; though, it could be made with most m&t jigs. Virtually all of my joinery is m&t-based.
The purpose for the post is to demonstrate one approach to updating, perhaps improving upon, a previously accepted practice- the window frame itself was instructive for me, but would be rather tedious for someone who has done more than one.
Also, I was uncomfortable supporting the weight of the glass with a traditional exposed m&t,
Once the client views the dry-build, I’ll sand progressively from 220 to 600, then finish with a Zinnzer sealcoat and sprayed Deft Acrylic – the specific intent is to enhance the Sapele grain and down play the sheen.