Cook the pasta in a large pot of boiling salted water until tender but still firm to the bite, stirring occasionally, about 4 minutes. Drain.Stir 2 cups of the cream and the lemon juice in a heavy large skillet to blend. Add the butter and cook over medium heat just until the butter melts, stirring occasionally, about 3 minutes. Remove from the heat.
Add the pasta and toss. Add the remaining 1/2 cup of cream, and Parmesan to the cream sauce in the skillet. Add the lemon zest, nutmeg, salt, and white pepper. Toss the pasta mixture over low heat until the sauce thickens slightly, about 1 minute.
Note: Cooks Illustrated suggests heating your individual serving bowls with hot water before plating. This will keep the pasta and sauce creamy longer. No one wants to eat congealed Christmas Fettuccine!
View step by step images of this recipe at my food blog ErinCooks.com