Lucky for me, no miter cuts were required for this project!
First up: the plinth. That's the decorative part at the bottom of the door frame. For the most part, the plinths in our house have very little decoration - some our just plain pieces of wood wider than the trim - and so the ones I found at the Blue Box fit the bill quite nicely: they have a little bit of carving which mirrors the top of the baseboards and the price was right too.
After installing the plinths aka nailing them into place, the sides of my door casing came next. All I had to do - thanks to the ingenius design of historic trim in our house -was measure the distance between the top of the plinth and the upper edge of my door opening, cut my boards to size and nail those into place as well.
I'd bought a length of plain "stop" trim to cap off the sides, just like on all the original door casings in our house. Since our bathroom and dressing room are a later addition to the house (years ago, a previous owner added a second story to the originally one-story part housing our kitchen), the ceiling is quite a bit lower as you can see. Thus, the husband and I are musing about bumping out the ceiling for a vaulted and airier headspace. It's not as bad as you'd think - especially since we painted everything white, both rooms feel light and spacious and you notice the low ceiling more like an afterthought.
A short length of a 1x2 board tops it all off. Voila! - historically accurate looking door casing. Oone side down, one more to go!
This whole project didn't take me that long. Of course, now we're back to the basics of caulking between boards and filling in those nail holes, priming and painting. It -never- ends, does it?