Get one the size of your dowel (assuming you are using round dowels).
Drill about 1/8" or so hole in your cabinet wall on either side where the brace will go. Add PL premium in this slot. Stick dowel in. Clamp cab walls together.
You'll want to practice using the forstner bit on scrap wood. There are ways to get it to only go to a certain depth, but that's out of my range of tool expertise. I just eyeball things like that and they usually turn out
You can use countersunk screws from the outside too.
