Bring a large covered pot of salted water to a boil.
Meanwhile, in a small skillet or saucepan on low heat, melt the butter. Stir in the cream and heat gently. Stir in the lemon juice and zest. Turn off the heat.
When the water boils, cook the pasta until al dente (2 or 3 minutes for fresh pasta, longer for dried). Reserve 1 cup of the hot pasta-cooking water and drain the pasta.
Place the hot drained pasta in a large serving bowl, add the lemon cream sauce, and toss. If the sauce is too thick, add some or all of the reserved hot pasta water. Toss in the grated Parmesan. Season to taste with salt and pepper.