In the last post I cut the tails and, from them, marked the pins. Here I'll finish the process.
I have made so many mistakes in the past (and probably will make many more in the future)... one of the most crucial lessons I've learned the hard way is to mark the waste. Mark it with slashes, black it out, dots, or a simple "x" like I did... it will lessen the liklihood of you cutting the wrong thing off, followed by gratuitous cursing and self-loathing, followed by preparing a whole new piece of wood. Learn from my mistakes.
I cut straight down for the pins until I hit the scribe line on both sides.
I then cut a bunch of saw kerfs through the waste. You can use a coping saw instead, and sometimes I do. I figure since I'd have to chisel clean the shoulder line anyways, might as well cut the coping saw out of the process this time... the kerfs make chiseling out that waste a little easier. Just to be careful, I mark the waste again.
I begin by chiseling from the "show side," the side intended to be the outside face. First, I make a few slight taps straight down at the knife line, then bring the chisel away from the line, bevel still facing away from the line, angled back, and drive the chisel towards the line.
Like so. I do not come in from the endgrain - this could cause a split that could carry through the grain beyond the shoulder. I go back to the knife line, chisel straight down, repeating this removal of waste maybe a third of the way through before I flip the board and repeat from the other side. Then back and forth, always working towards the center to avoid chipout, until the waste is gone.
And there it is! Most of the time, these joints are a little fussy and require care fitting them perfectly. You can see the pins and tails extend a slight bit beyond the edge of each face - this is common practice, as it is much easier to sand (or plane) down proud ends to match faces than faces to match edges.