In a large pot, bring salted water to a boil. Add the uncooked pasta and cook according to package instructions until al dente. Reserve about a cup of pasta water, then drain the rest and set the pasta aside.
In a large skillet, heat the butter and olive oil over medium heat. Once melted, add the thawed shrimp and season with salt and pepper. Cook for about 2-3 minutes on each side until they turn pink and opaque. Remove the shrimp from the skillet and set aside.
In the same skillet, add the chopped onions and sun-dried tomatoes. Sauté for about 2-3 minutes until the onions are soft. Add the minced garlic and cook for another minute until fragrant. Stir in the Dijon mustard and Cajun seasoning, mixing well.
Pour in the heavy cream, stirring continuously to combine. Allow the mixture to simmer for about 5 minutes, letting it thicken slightly. If the sauce is too thick, add a little reserved pasta water to reach your desired consistency.
Add the cooked pasta and shrimp back into the skillet, tossing everything together until well combined. Stir in the torn basil leaves and adjust seasoning with salt and pepper. Serve hot, garnished with freshly grated Parmesan cheese.
