Architrave where two door frames meet?

paperclap

I thought to do that, but then realised I'd never be able to hide that wood joint. Even with filler, it'll always come back.

So, I routed out just the centre portion of the back of the architrave, to bridge the gap. Granted, doesn't sit "flat" to the wall (angles in a bit), but it also meant I didn't need insane amounts of caulk in either side.

We didn't have our walls plastered, so only 4mm max difference. Yours may be worse!