Bring a large pot of water to a rolling boil. Add 2 tablespoons of salt (water should taste like the sea). Drop the pasta and cook until 1 minute shy of al dente, stirring occasionally.

While pasta cooks, place the butter pieces in a large, cold skillet. Set aside.

Just before draining, scoop out 2 cups of starchy pasta water. Reserve.

Drain the pasta (do not rinse).

Add the hot, drained pasta directly to the cold butter in the skillet. Toss with tongs until the butter melts and coats every strand.

Pour in 1/2 cup of the reserved pasta water. Toss vigorously. The sauce will look thin at first — trust the process.

Sprinkle in the grated Parmigiano-Reggiano in three additions, tossing well after each. Add the salt, pepper, and nutmeg if using.

Continue tossing and adding pasta water 1/4 cup at a time until the sauce is silky and clings to the pasta like a glossy coat. You may not need all the water. This takes about 2 minutes of active tossing.

Taste and adjust salt or pepper. Serve immediately in warm bowls. Garnish with parsley if desired.