Prep Your Ingredients & Cook the Pasta: Put a large pot of heavily salted water on high heat to boil. Cook pasta according to package directions for al dente. While it boils, whisk together all ingredients for the From-Scratch Cajun Seasoning in a small bowl. Before draining the pasta, reserve about 1 cup of the starchy pasta water.
Searing the Proteins for Maximum Flavor
Sear the Chicken & Sausage: Place a large skillet over medium-high heat and add the olive oil. Pat chicken chunks dry and season generously with about 1 tbsp of the Cajun seasoning. Sear in a single layer for 2-3 minutes per side until a deep golden-brown crust forms (it will not be fully cooked). Remove chicken to a plate. Add sliced andouille to the same skillet and cook for 2-3 minutes until browned. Add the sausage to the plate with the chicken.
Building the Authentic Cream Sauce
Sauté Aromatics & Deglaze the Pan: Melt the butter into the rendered sausage fat in the pan. Add diced onion and bell pepper and sauté for 4-5 minutes until softened. Add the minced garlic and cook for 30 seconds until fragrant. Pour in the chicken broth and use a spoon to scrape up all the browned bits from the bottom of the pan. Let it simmer for about a minute.
Create the Velvety Sauce: Lower the heat to medium-low and slowly pour in the heavy cream, stirring constantly. Add another ½ tablespoon of your Cajun seasoning. Let the sauce come to a gentle simmer (never a boil) and cook for 6-8 minutes, stirring occasionally, until it thickens slightly.
Finishing the Dish
Bring It All Together: Add the seared chicken and sausage (and any juices from their plate) back into the sauce. Heat through for a minute. Turn off the heat completely. Slowly sprinkle in the freshly grated Parmesan, whisking gently until the sauce is completely smooth. Taste and adjust seasoning if needed.
Toss, Garnish, and Serve: Add the drained pasta directly to the sauce. If using shrimp, add them now; the residual heat will cook them in 2-3 minutes. Toss everything together until the pasta is fully coated. If the sauce is too thick, stir in a splash of the reserved pasta water. Serve immediately, garnished with fresh parsley or green onions.