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.