In a large saucepan, warm the butter and cream over medium heat until the butter is melted. Simmer for 2 minutes. Whisk in garlic, salt and pepper.
Add 1 cup of Parmesan to the sauce and mix until melted through. Add the cooked fettuccine to the sauce. Toss a couple of times and add the remaining cup of Parmesan, tossing to combine. Sprinkle some chopped Italian parsley on top. Serve immediately.
Notes
Salt the water when boiling the fettuccine so it seasons the pasta.
Cook the fettuccine until just underdone so you can finish cooking it in the sauce.
Save some pasta water if you need to thin out the sauce.
Use freshly grated Parmesan cheese. Never buy pre-shredded Parmesan cheese as it contains wood pulp. Blocks of Parmesan cheese are also cheaper.
Use a high fat content cream as it thicken when it cools so you don't need a roux.
Serve immediately or the pasta will clump together.