After removing the edge material with a router and an plane the first step is detailed layout.
This is followed by some rip cuts at a slightly awkward angle.
A coping saw is then used to remove the bulk of the material between the tenons. This is tidied up with a block plane.
The two end tenons are from thicker timber and required some materal from the bottom. I used a rip saw at an even more awkward angle.
The last and most fiddly step is fitting the joint. This is tricky because the whole point of the process to keep the table flat which relies on a tight fit. At the same time however it needs to be loose enough to allow lateral movement and be easily fit.
At this point I ran out of time...