[Zeke]

"I'll bet that there are a million tutorials on YouTube."

There are a lot but most of them are pretty amateurish.

One thing that is helpful when you have to do this by hand is to locate and screw the striker plate on top of the jamb surface. Double check that this is where you want it and then heavily scribe around the strike to establish your cut. Remove the strike and use the chisel every 1/4" to make a cut as deep as the thickness of the strike (not much as most are around 3/32nds). Rake out the chips and clean up by entering the mortise from the edge leveling out the mortise.

When I'm doing little strikes like those for flush and surface bolts, I always screw them down first to establish the location. If you need to make an adjustment, this is the time to do it. Fill the holes you just drilled with a small dowel or fat toothpick and re-do.