The main weakness of a normal miter joint is that there is no face-grain glue surface. The mitered half lap joint overcomes this limitation by combining a half lap joint with the miter joint, giving it a great deal of strong glue surface, while maintaining the appearance of a miter joint from the front.

This is shown on a 1”x2” piece of lumber, but it can be scaled to any width or thickness. The important thing is that the angles are always at 45° and the lap joint is half the thickness of the piece.