I think the diagram above is a little deceptive in implying a recess is made. Much of the time the intention is just toi flatten off the top of a cast-in boss in a circle around the head of a bolt. Putting in a recess can create a problem of spanner access if not useing cap heads.
Rather than modify a drill it is common practice to make a simple spotfacer in silver steel the diameter of the desired spotface as follows. 1) drill end of silver steel bar the size of the hole, 2) make 2 saw cuts as an X across the end, 3) file relief on the end back from the cuts like the end of an endmill 4) harden and temper, 5) insert guide pin in the hole you drilled at the start. 6) use gently.