Grate the parmesan cheese into a bowl.
Use freshly grated parmesan cheese.
Fill a large pot about two-thirds full of water. Add 1 teaspoon of salt and put on high heat.
Prepare the sauce while the water heats. Melt butter in a medium saucepan over low heat. Add the cream, the remaining half-teaspoon salt, and the pepper. Heat and stir until steam rises, but do not boil.
the egg yolk
Separate an egg yolk into a small bowl. Add 3 tablespoons of the hot cream mixture and stir with a fork. Whisk the yolk into the sauce and heat thoroughly.
Mixing a small amount of hot cream into the
egg yolk prevents the egg from scrambling.
When the water is at a rolling boil, add the fettuccine, stir, and cook until al dente. Drain the pasta and quickly return it to the pot.
the sauce, cheese.
Add the hot cream sauce and half the grated cheese to the pasta and
stir vigorously. The hot pasta and sauce will melt the cheese. Once
the first half of the cheese is melted, fold in the rest of the cheese.