Hinge Mortise Jig Set. Then let a trim router do all the work. The end stop on the threaded rod and the mortise width stop can be set quickly.
Mortising a Hinge with a Chisel - Fine Homebuilding (Jim Lucas)
The heart of this jig is the two-piece platform. It provides a wide surface to steady the router base. Great Savings & Free Delivery / Collection on many items.
Install or remove the corner inserts, as appropriate: Depending on the inserts used, jigs can cut mortises with rounded or squared corners (squared corners must be finished later with a chisel).
It uses the hinge to set the jig for a perfect fit.