In a large pot of boiling salted water, cook the pasta according to package instructions; drain well and reserve 1 cup of pasta water.

In a large skillet over medium high heat, melt two tablespoons butter. Add shrimp, salt and crushed red pepper, and cook for 2-3 minutes per side, or until shrimp is opaque pink. Remove from heat and set aside on a plate.

Lower the heat to medium, and in the same skillet, add the remaining butter and garlic and cook until fragrant, about one minute. Add the parmesan cheese, lemon and pasta water and stir to combine to create a sauce.

Transfer the spaghetti to the skillet and toss with the sauce. Add the shrimp on top and toss to combine.

Garnish with chopped parsley and serve immediately.