The tabletop with the tenons cutout and ready to be pinned

The center pin remains stable while the edges are elongated to allow for seasonal wood movement. 

Not shown is drilling out the breadboard with a drill press. Once the hole in the breadboard is driller, fit the joint together and use the same drill bit you plan to use to mark the center point of the hole. Once the center point is established with the center point of the drill bit, you can offset the hole in the mortise by a small amount (depending on the hardness of the wood species and "spring" in the joint). For the purposes of this joint, we sprung the joint by roughly 1/64" and offset the hole by a little more more than 1/16". Mark your center point first.

Make sure you offset the hole so that once the pin is hammered in, it pulls the joint tight rather than pushes it apart!

Here you can see a drawbore pin (a Lie Nielsen Drawbore Pin in this case) holding the joint together and "springing" the joint. From here we'll mark the edge holes with the drill bit we plan to use and lightly hammer them to make a mark. Once you have the center point marker, you can offset by a small amount and drill the elongated holes. In this case, we were using 3/8" dowels and offset by roughly 1/16". The holes were elongated to a little over an inch (sorry for not taking more pictures).

Use a sander, plane, chisel, whatever to taper the pins so that the end you're hammering in is pointed and can more easily navigate the edges. I freehanded these using a block plane to a rough point. I'll do another Monday 101 on how to create your own pins.

I have video but it's not in the correct format. I'll see if I can update and upload for the next revision. Take your time, starting at the center pin, and hammer the pins around the bend and into place. If you listen carefully you'll hear the difference in the sound as the pin makes the turns. Slow light taps are your friend here. If you're too rough you may splinter the pin and have to pull (or worse, drill) the pin out and start over. 

Once the pins are all hammered in, you can use a flush cut saw to cut them flush to the surface. If you don't have a flush cut saw, you can use a thin refrigerator magnet you get from everywhere as promotional items and stick it to your saw to give you a small offset. Once the cut is made, use a sharp chisel or block plane and a pairing motion to slice the grain and flush up the pin.

Looking good here.

We left the breadboard longer so that it could be trimmed once the joint was ready to assemble.

Hand tools are your friend here, specifically a crosscut saw. Draw your line, stay just shy of it, establish your kerf, and cut off the excess. 

Use a hand plane or a sander to clean up any excess you had from your cut line. I used a #62 here to clean up the end grain.

Tabletop assembled and ready for routing, sanding, and finishing.