Start by prepping all your vegetables. Chop all as close in size as possible. Depending on personal preference, you can chop to the size you like. Do not mix together at this point, you will need to sauté them for different lengths of time. See notes above to safe time on this step.
Cook sausage in its own skillet. Make sure sausage is crumbled and cook it through completely. Once cooked, drain sausage and place in bowl and set aside.
While the sausage is cooking, in the other large skillet, melt a tablespoon of butter. If you are using raw carrots, start with cooking them (they take a little longer to cook). If not, start to sauté onions, after a few minutes add in the celery. Just cook until lightly sautéed. You don't want them overcooked. The will cook more once you place stuffing in the oven. If you are using shelf stable carrots just add them in after the onions and celery are cooked. Since they are shelf stable, they are already cooked. Remove mixture from heat.
Combine sausage with onion, celery, and carrot mixture. You may need to use 2 different skillets or large bowl since the mixture becomes quite a lot once you start to add in the stuffing mix.
Start to add the stuffing to the mixture. Add a small amount and a time so you can blend the mixture well. As you are mixing, add in the chicken broth. Once again, a little at a time so you don't add too much liquid. You will only need about 3/4 of the chicken broth container. Save the rest for after you bake in case you want to add a little more once it is cooked. Add what you like, this is personal preference on how moist you like your stuffing.
Once mixture is complete, place in a greased 9x11 dish or large casserole dish.
At this stage, you can cover and put in the fridge until you're ready to bake. If you leave it overnight, just take it out about 30 minutes before you want to bake so it's not ice cold going into the oven.
Bake for approximately 30-35 min at 350 degrees or until top of stuffing browns a bit. Keep the pan lightly covered for the first 20 minutes or so and then remove cover for the last few minutes so the top browns a bit. Since all items are cooked before baking, you don't have to worry about reaching a certain temperature, but you will want to make sure it is heated through.