Preheat oven to 250, spread cornbread out in an even layer on rimmed baking sheets and dry in oven for 50-60 min. Beat eggs, half and half, and broth together in a large bowl then add cornbread and toss gently being careful not to break up pieces of bread. Cook sausage in a skillet, drain grease and then empty into a bowl. Add the butter, the onions and celery to the pan and cook until they are softened. Then add the herbs, garlic, salt and pepper and cook until fragrant. Add back the sausage and mix all together. Then add sausage mixture to the bread mixture and stir gently so as not to break up the bread pieces much. Spray a disposable 16x12 in aluminum roasting pan with non stick spray, and add dressing to the pan, cover with foil, and refrigerate until ready to use. Bake in a 400 degree oven with foil on for 30 minutes, and then remove the foil and bake for an additional 15 minutes.