For the roux, in a heavy 10-inch skillet combine the oil and flour. Place the skillet over medium-high heat and cook for three minutes, mixing constantly and thoroughly with a long-handled metal whisk or a wooden spoon until smooth.

Reduce heat to medium, and continue cooking the roux, whisking or stirring constantly so it doesn’t scorch, until it turns a peanut-butter brown, about nine minutes. Remove from heat and continue whisking constantly until the roux stops getting darker, about three minutes. Set aside.

In a heavy 8-quart saucepan, melt the butter over medium heat. Add the garlic and cook until it just starts to turn golden brown (the color of a pumpkin-pie filling), about one minute, stirring constantly. Stir in the onions, sweet peppers, celery, and bay leaves and cook and stir for one minute.

Add the tomatoes, sausage, Creole seasoning, and thyme to the pan, stirring well. Cook until all the vegetables are tender, about five minutes, occasionally stirring and scraping the pan bottom clean.

Stir in the stock and parsley, mixing well, and bring to a boil over high heat. Reduce the heat and simmer for 15 minutes.

Gradually add the reserved roux, stirring constantly until all the roux is thoroughly blended in.

If you’re making the gumbo ahead, which is preferable, let it cool at this point, then cover and refrigerate it until it is time to reheat and proceed with the recipe.

Next, stir in the shrimp and crabmeat and let the shrimp cook about half way, about two minutes. Do not overcook the shrimp.

Add the oysters and bring to a boil, skimming any foam. Continue cooking just until the oysters are plump and their edges curl, one to two minutes more.

Remove from heat. Season the gumbo with more kosher salt and pepper if needed.

Serving Suggestions: If prepared ahead, which is preferable, do not add more salt and pepper at this time. Instead, let the gumbo cool down and refrigerate in a covered container. Just before serving, reheat until all the ingredients are just hot so the seafood doesn’t overcook, then season with more kosher salt and pepper if needed.

If serving immediately, season the gumbo with more kosher salt and pepper to taste before dishing out. Serve the gumbo, garnished with a light sprinkle of green onions, in heated cups or bowls over rice, or pass the rice at the table, along with hot or mildly hot pepper sauce and saltine crackers or crusty French bread.