1The original recipe calls for an oven temperature of 425 and baking for 10 to 12 minutes. I used an oven temperature of 350 and baked it 1/2 hour.
Oil a shallow 3 qt. baking dish. I didn't bother oiling my large Pyrex bowl.
2Cook pasta according to package directions.
Meanwhile, heat 1 Tbsp.oil in a large skillet over medium-high heat. Thinly slice the kielbasa or smoked sausage. Brown the sausage, about 1 minute on each side. Remove from skillet.
3Heat 1 Tbsp. oil in skillet over medium-low heat and cook onions, peppers, and garlic, covered, until tender, 8 to 10 minutes. Stir occasionally.
Sprinkle flour over the onion mixture and cook, stirring, for 1 minute.
4Whisk in the milk and bring to a simmer. Whisk in the cream cheese and Cajun seasoning until blended.
Stir in the Cheddar and Gruyere and simmer, stirring occasionally, until cheese is melted and the mixture is smooth and slightly thickened, 1 to 2 minutes.
5Toss the pasta with the cheese sauce and transfer to baking dish. Bake until golden brown, 10 to 12 minutes at 425. (Or 1/2 hour at 350.)