Cook pasta in generously salted boiling water according to package directions. Before draining, reserve 1 cup of the pasta water. Drain and set aside on a plate or in a large bowl until ready to use.
Meanwhile, in a large skillet over medium heat, melt butter and olive oil. Add shrimp and season with salt, pepper and Cajun seasoning. Cook until pink, about 2 minutes per side, then transfer to a plate.
Add 3 tablespoons of butter to the skillet and melt, swirling around to coat. Stir in minced garlic and cook for about 30 seconds to a minute. Whisk in about 1/4 cup of the pasta water and stir constantly to deglaze (loosen and scrape up all those lovely brown bits of flavor) the pan if needed, then stir in flour and cook for about one minute or until golden.
Whisk in milk, cream and remaining pasta water and simmer for several minutes until thickened (sauce should coat the back of a spoon). Remove from heat and stir in Parmesan cheese until melted.
Toss the cooked pasta and shrimp with the sauce to coat.
Serve immediately, garnished with diced tomatoes and fresh chopped parsley.
Instead of shrimp, use chicken breast or spicy sausage.
Add more or less cajun seasoning based on your liking.
I suggest fettuccine or linguine, but I also love penne, rigatoni or even spaghetti.