Boil a large, salted pot of water for the pasta. Cook pasta according to package directions.
Meanwhile, add butter and olive oil to a skillet on medium heat. Sauté onions for 5 minutes or until they're lightly browned if you wish (this gives extra flavor).
Stir in the Dijon mustard, sun-dried tomatoes, and garlic to the pan and cook for about a minute.
Add the cream and Cajun seasoning, and cook for a few minutes until you have a nice, smooth sauce.
Add the shrimp in, and cook for about 5 minutes or until the shrimp are cooked and the sauce is reduced to your liking. Season with salt & pepper if desired, add the fresh basil, and toss the drained pasta with the sauce. Serve with freshly grated parmesan cheese.