Cook the fettuccine in a large pan of salted boiling water until al dente. Before draining, reserve a mugful of the pasta water.
Meanwhile, melt the butter in a large frying pan over a medium heat. Add the garlic and cook for 1 minute, making sure it doesn’t brown.
Pour in the double cream, bring it to a gentle simmer and cook for 2-3 minutes until it starts to thicken slightly.
Turn the heat down low, then add the Parmesan, and parsley and stir until the parmesan melts into the cream and you have a smooth sauce.
Add the cooked fettuccine straight into the sauce with a splash of the reserved pasta water. Toss everything together for a minute or two until the pasta is completely coated and the sauce is glossy and creamy.
Season generously with black pepper and add salt if needed. If the sauce gets too thick, loosen it with another splash of pasta water.
Divide between bowls, then finish with some extra Parmesan, and plenty of black pepper.