That joint is just made to be cut on the radial arm saw. Leave your saw a touch high so you can clean up your bottoms nice and flat with a chisel or shoulder plane, and then cut your angle.
If you don't have a radial arm saw, you could easily cut them by hand too. Just use a good crosscut saw to and rip saw to make the notch, then make the ankle cut with a crosscut saw or miterbox.
My preference is the radial arm saw though. Many people believe its use is outdated, but to understand it, is to love it.
I have no intention of traveling from birth to the grave in a manicured and well preserved body; but rather I will skid in sideways, totally beat up, completely worn out, utterly exhausted and jump off my tractor and loudly yell, "Wow, this is what it took to feed a nation!"