Bring a large pot of water to a roaring boil. Season with one teaspoon kosher salt. Add the fettuccine and cook according to the length of time suggested on the package so the pasta is al dente. Stir immediately after adding it to the water and frequently while it is boiling.
1/2 pound fettuccine
In a large skillet over medium heat, melt two tablespoons butter. Add the garlic to the melted butter and cook until just fragrant, less than 30 seconds. Add the shrimp and cook for six minutes, tossing until the shrimp become opaque. Remove the shrimp with a slotted spoon and transfer to a plate, tenting with foil.
2 garlic cloves, 1 pound shrimp
Add the remaining two tablespoons butter, and melt. Whisk in the heavy cream. Bring it to a simmer, and turn the heat down low. Cook for 15 minutes, stirring occasionally. You should see occasional bubbles.
2 cups heavy cream
Stir in the Parmesan cheese until it melts. Season with salt and pepper, tasting and adding more as needed. I typically add about 3/4 teaspoon salt and almost 1/4 teaspoon black pepper. The seasoning at the end really pulls together the dish, so be sure to play with this.
1 cup Parmesan cheese, 1/4 teaspoon kosher salt, fresh black pepper
Toss with fettuccine, return the shrimp to the pan, and enjoy immediately with a sprinkle of fresh parsley if desired.