Recipe courtesy of Fresh from Louisiana: The Soul of Cajun and Creole Home Cooking
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Fill a large pot with water and add the table salt. Place over high heat and bring to a boil. Add the pasta and cook until just al dente. Remove from the heat and strain. Reserve for later use.
In a large pan with a tight-fitting lid over medium-high heat, add the oil. Add the sausage, onion, celery, and bell peppers and cook until the onion turns translucent, about 5 minutes. Add the garlic, rosemary, white wine, and spinach and stir to combine. Let the alcohol burn off as the spinach begins to wilt. Add the cream and stir. Decrease the heat to a simmer, cover the pan, and cook for 15 minutes, stirring every 5 minutes.
Uncover the pan and stir. The spinach should be wilted and the cream will have begun to reduce. Continue simmering the mixture as the sauce thickens. Add the Cajun seasoning and hot sauce to taste. Turn off the heat until ready to serve.
Chop half the oysters and leave the remaining oysters whole. Just before serving, bring the cream and spinach mixture back to a simmer and add the oysters and ¼ cup (60 ml) of the oyster liquor. Gently simmer the oysters in the creamy bath until they are delicately poached and the edges begin to curl and wrinkle, about 5 minutes.
Add the precooked pasta and simmer until the pasta is fully cooked, about 5 minutes. Add the cheese and green onions and stir into the sauce. Turn off the heat. Taste and add kosher salt, if needed.
Serve the pasta in shallow bowls with crusty French bread for dipping in the rich sauce.