A simple open mortise and tenon joint that's been planed smooth by a 25° included angle blade in a Veritas Low-Angle Jack Plane. The wood is Hard Maple and the glue is Elmer's Wood Glue Max(A product which I really like).

First what you see...

What it looks to the 'naked eye'

Then what a Canon T3i with a reversed 18-35mm lens sees...

Up close and personal