(Please excuse the picture quality. I think I left my camera's charger in St. Louis...or Cincinnati...or Philadelphia.)
Start with a piece of boxing that approximates the final dimensions.
Create the groove and shoulder on your table saw (sorry) by tilting the blade and running the blank through vertically and then horizontally.
Fit the square boxing into the plane blank. I use a block rabbet plane. (Note: when fitting the boxing the iron's edge of the block rabbet plane must project from the plane's side, or you will not be able to cut square.)
Knock off the the corners so you have a surface on which you can...
Yada, Yada, Yada...
Square the planes and add finish.
Did you make it this far without knowing what purpose the boxing serves? We'll touch upon it soon.In the mean time, be excited...
SAPFM semi-annual meeting this weekend!