Step 1: Prepare Your Mise en Place
Grate the Parmesan cheese fresh. Mince the garlic if using. Bring the butter to room temperature.
Step 2: Cook the Fettuccine
Fill a large pot with water and add kosher salt generously – the water should taste like seawater. Bring to a rolling boil over high heat. Add the fettuccine and cook according to package directions until al dente. Reserve 1 cup of pasta cooking water before draining.
Step 3: Create the Base Cream Sauce
In a large, heavy-bottomed skillet or saucepan, melt the butter over medium-low heat. If using garlic, add it now and sauté for 30 seconds until fragrant. Pour in the heavy cream and whisk gently to combine. Allow the mixture to warm through without boiling.
Step 4: Build the Cheese Sauce
Gradually add the grated Parmesan cheese to the warm cream mixture, whisking constantly to prevent clumping. If the mixture seems too thick, add pasta water one tablespoon at a time until you reach the desired consistency.
Step 5: Combine Pasta and Sauce
Add the drained fettuccine directly to the cream sauce in the skillet. Using tongs, toss the pasta gently to coat every strand with the creamy mixture.
Step 6: Final Seasoning and Serving
Season with white pepper, nutmeg, and salt to taste. Serve immediately in warmed bowls, garnished with additional grated Parmesan and fresh parsley.