Preparation Combine onions, bell peppers, and celery in a medium-size bowl and set aside. In a small bowl combine next 7 ingredients for seasoning; mix well and set aside. Heat the oil in a large skillet over high heat until it starts to smoke, about 5 minutes. Gradually add the flour, whisking constantly with a metal whisk. Continue cooking and whisking until roux is dark red-brown to black, 2-4 minutes. Immediately add half the vegetable mirepoix and stir well, switching to a spoon if necessary, 1 minute. Add the remaining vegetables, continuing to stir, about 2 minutes. Add the seasoning mix and continue to cook, about 2 minutes. Add garlic, stirring well for another minute. Remove from heat. Place the stock in a 5 1/2-qt saucepan or Dutch oven and bring to boil. Add roux mixture by spoonfuls, stirring until dissolved in between each addition. Bring back to boil. Add andouille and return to boil again; continue boiling for 15 minutes, stirring occasionally. Reduce heat and simmer 10 minutes. Add the shrimp, undrained oysters, and crab meat. Return to boil, stirring occasionally. Remove from heat, skim oil from surface, and serve over rice.