I have no real recipe, I just eyeball it and taste it to make sure it is as close to my grandmother's as possible (she doesn't have a recipe either, just told me the basics of what goes into it several years ago, and mine is closer than anyone else has gotten!)
I get four packets of white cornbread mix (some weird brand, that says "from the maker's of Martha White" on it - helpful, I know

) and make it the day before Thanksgiving. It has to be the plain white cornbread mix, it is NOT the same with yellow, and don't get any that is presweetened like Jiffy. Jiffy has its place, but that place is not in my dressing.
The morning of Thanksgiving, after the turkey is out of the oven (because you need the drippings), I crumble up the cornbread and put it in a huge mixing bowl. I saute onions and celery in butter and a touch of rubbed sage (I have no exact measurements, I just go by muscle memory I guess) until soft. I'd guess one full medium to large yellow onion and five or six celery stalks?? I just sort of start chopping and see how it looks. One year I chopped my onion and celery the day before, and the dressing did not taste right, so I don't recommend doing that. I'll never do that again!
The onion/celery mixture goes into the crumbled up cornbread, followed by more rubbed sage, and a teaspoon or two of baking powder. I ladle on turkey drippings until it's fairly wet, and mix. I taste it to make sure there's enough sage flavor (too much makes it sweet, yuck! but too little makes it bland - there's a fine line) and add more as needed, same with the turkey drippings - you don't want dry dressing! I also keep some chicken stock nearby if I need more liquid (because I save some of the turkey drippings for gravy), but I don't usually need too much of that, if any. I don't add any salt, b/c what comes from the turkey takes care of that (my turkey is rubbed down with only unsalted butter and sea salt, with butter shoved up under the skin.)
Then it all goes into a 9x13 glass pan (the same one the cornbread was baked in the day before), more drippings poured over the top if needed, and it bakes for at least 30 min on 350, sometimes longer, until the edges start to brown.
Everyone always goes nuts for this, I make a huge batch so I can have leftovers. Because it's a family recipe, it's difficult to share exactly what to do b/c *I* know what tastes right, and how it's supposed to look, but it can be hard to judge when making it for the first time. My stepmom cannot get it right, she always ends up making it sweet and no one touches it. If she didn't already hate me, the fact that I can make it and she can't would push her over the edge, LOL!!
But it's been made for over 100 years by my grandmother and her mom before her, so it's a simple Ozarks classic for sure. I've never had anyone I've ever served it to NOT go back for seconds or thirds.