Slice the andouille sausage into medallions, set aside. If using uncooked chicken-cut chicken into bite-size pieces; if using cooked chicken, shred pull or chop chicken. Place in a bowl and mix in Creole seasoning and set aside.
Measure out the flour and vegetable oil.
Mix the Herb and Spice Blend in a small bowl and set that aside.
Chop the vegetables and set aside. Chop the garlic and set aside in a small bowl
Place the chicken stock in a stock pot and start heating it on low. Keep it covered and on low so it does not reduce.
In a large cast-iron Dutch oven over medium-high heat sauté the sausage until browned and rendering some of its fat. Scrape the brown bits off the bottom. When the sausage is nicely browned, remove it from the pan back to its bowl, leaving the renderings in the pan. About 5 minutes.
Maintaining the medium-high heat, add the vegetable oil to the frying pan. When the oil is shimmering whisk in the flour to make a dark roux. About 10 minutes.
As soon as the roux is dark enough add the veggies in about half or a third at a time and stir to completely mix the veggies with the roux.
Continue to cook over medium-high heat, stirring frequently and scraping the bits off the bottom, careful not to let it burn or scorch. This will take at least 15 to 20 minutes.
Add in the garlic and green onions and continue to cook until aromatic, usually a couple of minutes.
MIx in about half the spice mix and the 2 bay leaves; add back the sausage, mix well and cook for another five minutes.
Turn up the heat on the stock pot and bring the chicken stock to a rolling boil.
Using a slotted spoon, mix in the veggie/sausage mix, one spoonful at a time, stirring each spoonful until everything is blended and mixed with the stock, making sure it returns to a rolling boil in between each spoonful. Continue this, one spoonful at a time until all the veggie/sausage mix has been added to the stock. About 10 minutes.
If using raw chicken, add it now, a few at a time, stirring them into the stock in a similar fashion as you did the veggies, letting it come back to a rolling boil between each spoonful. If you are going to throw in a couple of chicken wings, now is the time. If using cooked chicken from making stock, we will add that later.
Add a little more spice mix, stir well.
Turn the heat down to low, cover the pot and simmer for about an hour, stirring occasionally.
Add the cooked chicken from making the stock now, a little at a time. Stir to combine and simmer, uncovered, for 15 to 30 minutes.
Prior to serving, skim off the grease which has floated to the top. Give the gumbo a good stir then taste for seasoning-add a little more of the spice mix or some more salt and black pepper, if needed.
Remove the bay leaves and serve over white rice.