Meanwhile, toss shrimp with pepper flakes and a bit of kosher salt.
In a cast iron skillet, melt the olive oil and one tablespoon of the butter. Add the garlic and shrimp and cook on both sides until the shrimp turn pink. Add the lemon juice.
Remove the pan from the heat and add the rest of the butter, sliced, and stir until a sauce develops.
Add the pasta, and parsley, and toss until the sauce envelops the pasta. Top with the Parmesan cheese.