Soften the butter: Soften 4 tablespoons unsalted butter in a small bowl by microwaving in 10-second intervals until very soft but not melted (about 20-30 seconds)Mash the softened butter into a smooth paste with a fork.
Add the cheese: Mix 2 ounces Parmigiano-Reggiano cheese(very finely grated) with the butter into a thickened, frosting-like texture. Season with a pinch of salt, and transfer to a large heatproof bowl.
Cook the pasta: Once the water is boiling, season generously with salt and cook 8 ounces fresh fettuccine until al dente. About 30 seconds before the pasta is done, reserve ½ cup of pasta water. Add about 2 tablespoons of the pasta water to the butter-cheese mixture and whisk until nicely smooth and creamy.
Add the pasta: Using tongs, immediately transfer the hot pasta to the bowl, tossing frequently until the sauce begins to thicken and coat the pasta.If desired, add a little more pasta water to loosen the sauce. Season to taste with additional salt, if necessary, and some freshly ground black pepper (if desired).
Serve: Divide pasta amongst two serving bowls. Top with more cheese, if desired. Serve immediately, and enjoy.Note: This recipe comes together very quickly, so it's imperative you start eating as soon as it's done, as the sauce will cool down and thicken very quickly too.
Notes
* Grate the cheese yourself: Very finely grated cheese is a must here as it will allow the sauce to come together smoothly without clumping. To do so, use a blender or food processor to blend bite-sized chunks of the cheese until very finely grated, powdery, and fluffy in texture.Black pepper is listed as optional but can be a nice touch.Fresh pasta will deliver the most luxurious result, but you can also use dried. Just make sure to buy dried egg fettuccine, which comes in nests, and best mimics fresh pasta.Original recipe credited to Alfredo Di Lelio via a Reddit post.