Throughly combine the seasoning mix ingredients in a small bowl and set aside. In a separate bowl combine the onions, celery, and bell peppers.

In a large skillet (preferably cast iron), heat the oil over high heat until it begins to smoke, about 4 minutes. With a long handled whisk, gradually mix in the flour, stirring until smooth. Continue cooking, whisking constantly, until roux is dark brown, about 3-5 minutes. Remove from heat and immediately stir in the vegetables and 1 tb. of the seasoning mix with a wooden spoon. Continue stirring until cooled, about 5 minutes.

In a 2 litre saucepan bring 2 cups of the stock to a boil over high heat. Gradually add the roux and whisk until thoroughly dissolved. Reduce heat to low and cook until flour taste is gone, about 2 minutes, whisking almost constantly. Remove from heat and set aside.

In a 4 litre saucepan melt half c butter over medium heat. Stir in shrimp and the green onions; saute 1 minute, stirring almost constantly. Add the remaining stick of butter, the stock mixture and the remaining 1 cup stock. Cook until butter melts and is mixed into the sauce, about 4-6 minutes, constantly shaking the pan in a back and forth motion.

Add the remianing seasoning mix, stir well and remove from heat (if sauce starts to separate, add about 2 tb. more of butter or water and shake pan until it combines). Serve immediately.