Bring a large pot of salted water to a boil. Add fettuccine and cook according to package instructions (8-10 minutes). Reserve about 1 cup of pasta water, drain fettuccine, and let it steam dry.

In a large skillet, melt butter over medium heat. Whisk in heavy cream and simmer for 2-3 minutes. Gradually add Parmesan cheese, stirring until melted and smooth. Season with salt, pepper, and nutmeg if desired.

Gently fold in crab meat into the sauce, cooking for an additional 2-3 minutes until heated. Keep the heat moderate to avoid curdling.

Add the drained fettuccine to the skillet. Toss to coat the pasta evenly in the sauce, adding reserved pasta water if necessary to adjust consistency.

Transfer to serving dishes. Garnish with parsley and lemon zest if desired. Serve immediately.