In a medium-heated heavy pot or dutch oven, fry sliced sausage with a little EVOO and set aside.
In the same pot, add butter and about 1/4 cup of EVOO. When butter melts, quickly whisk in flour until fully incorporated. Using a wooden spatula, stir continuously (to prevent flour from scorching) until roux is brown, about 10 minutes.
Add trinity and garlic to the mix and cook for another 5 minutes or so. Make sure the roux doesn’t stick to the bottom of the pan, so add more EVOO if you need to.
Now, add the stock to deglaze the pot for a couple of minutes. Then, sprinkle in the Cajun seasoning mix and bring to a boil. Let reduce uncovered, still in medium heat, for about 40 minutes or until liquid reaches a gravy-like consistency.