Bring a large pot of water to a boil and add 1 tablespoon of salt. Allow this to dissolve then cook the fettuccine to al dente according to the package instructions (or about 2–3 minutes for fresh pasta). Stir occasionally so it doesn’t stick and reserve 1–2 mugs of the starchy pasta water just before you drain the pasta.
In a medium bowl, add the Pecorino Romano and a little pasta water. Whisk by hand until it becomes a smooth, runny cream.
Place a large pan over low heat and melt the butter. Using tongs, transfer the pasta straight into the pan allowing some of the pasta water to seep in. Toss well so the butter coats the pasta then set the pan over the pot of hot pasta water (to create gentle steam). Pour in the Pecorino cream mixture and gently toss the pasta with tongs.
Keep mixing until the sauce thickens and coats the pasta evenly. If the mixture looks too watery, place the pan back on the stove over very low heat and continue tossing until glossy and creamy.
