Follow the steps in order for the best result.
In a large stockpot, place the whole chicken.
Add 8 cups of water, ensuring the chicken is fully submerged.
Introduce the butter and chicken bouillon to the stockpot.
Peel one of the yellow onions, coarsely chop it, and add it to the pot.
Bring the pot to a simmer over medium heat, allowing the chicken to cook for approximately 1 to 2 hours, or until fully cooked.
Remove the pot from the heat source.
Carefully remove the chicken from the pot, setting it aside on a cutting board to cool; reserve the chicken stock.
Once the chicken is cool enough to handle, debone it, discarding the bones.
Finely chop the remaining onion, bell pepper, and celery, then set aside.
In a separate large stockpot, heat the canola oil.
Gradually add the flour, one tablespoon at a time, whisking continuously and slowly for about 20 minutes to create a roux.
Continue cooking the roux until it achieves a chocolate brown color, being cautious not to burn it; discard and restart if black specks appear.
Incorporate the chopped onion, bell pepper, and celery into the roux, stirring for approximately 3 to 4 minutes until softened.
Pour in the 6 cups of reserved chicken stock (from cooking the chicken) and stir well.
Slice the smoked sausage and add it to the stockpot.
Season the gumbo with Tabasco sauce, cayenne pepper, salt, pepper, bay leaves, and parsley.
Cover the pot, reduce the heat to low, and simmer for about 15 minutes.
Add the deboned chicken meat and cook for an additional 5 to 10 minutes, or until the chicken is heated through.
Serve the gumbo in bowls over white rice.
Garnish with additional dried parsley, if desired.