Prep all ingredients and season the shrimp with Cajun seasoning and olive oil in a bowl, tossing to coat.
Bring a large pot of water to a boil, adding 1 tablespoon kosher salt.
Heat a large skillet over medium-high heat.
Add penne pasta to the boiling salted water and cook until al dente. Reserve 1/2 cup pasta cooking water before draining.
Add butter to the hot skillet and melt, then add shrimp in a single layer. Cook until golden brown on each side, turning once.
Transfer cooked shrimp to a plate and reduce skillet heat to medium.
Pour heavy cream into the skillet, scraping the bottom with a wooden spoon to release browned bits. Let cream bubble around edges.
Reduce heat to low and stir in parmesan cheese until melted.
Add cooked pasta and shrimp to the skillet and stir to coat in sauce.
If sauce is too thick, thin with reserved pasta water, one tablespoon at a time, to desired consistency. Adjust salt if needed.