I am guessing you desire to walk down the hand made path... or saw and chisel to be correct.
If you plan to make squillions of joins, it's hard to bypass a jig.
I use the
Leigh D4R jig... not cheap but nearly as versatile (in layout) as a hand job... and their instruction manuals are reputed to be one of the best... many alternatives out there (for volume builds).
If your first cut is too short... Take the second cut from the longer end... LBD