Preheat the oven to 350ºF. Spray a 9x13 with cooking spray.
Over medium heat, squeeze the sausage (if it's in the casings) and cook until almost done (you don't want it too dry). If the sausage is sticking to the pan, add some avocado or olive oil. Remove sausage and add to the bowl of 9x13 pan (whatever you're mixing the stuffing in).
Add 2 tablespoons of butter to the pan, melt, and add the onion and celery. Stir until the onion is translucent (see-through) starting to brown. Add the garlic, 1/2 teaspoon of chopped fresh rosemary, 2 teaspoons of chopped fresh thyme, 1 teaspoon of chopped fresh sage, and stir for another 2-3 minutes. Your home is going to smell amazing right now.
Add the onions and celery to the sausage and then add the sourdough, melted butter, ground sage, the sprigs of rosemary, sage, and thyme (chop them before you add). Stir it around well. Then slowly add the 2 cups of chicken broth. Assess the stuffing mix. Add more broth if needed. You don't want it swimming with a pool of liquid, or have it too soggy. If you over-pour, it's salvageable...it will just take longer to cook.
Wrap your casserole dish with aluminum foil and bake for 30 minutes. Remove the foil, stir it, and bake uncovered for another 15-20 (depending on how liquid is in there). If it looks a little dry at the 30-minute mark, add a bit more broth and stir. At this point, you can taste and adjust seasonings as well. Does it need more salt? Pepper? Sage? Everyone likes their stuffing differently, so this is a great time to customize it.
Top with some fresh parsley and serve. If you're waiting for turkey and all the fixin's to be done, cover with foil so it doesn't dry out.