Slice the top off the head of garlic to expose the individual cloves. Drizzle with olive oil and wrap in aluminum foil. Roast in the oven for about 30-35 minutes, or until the cloves are soft and caramelized. Remove and let cool.
While the garlic is roasting, bring a large pot of salted water to a boil. Add the fettuccine pasta and cook according to the package instructions until al dente. Reserve 1 cup of pasta water, then drain the pasta.
In a large skillet over medium heat, melt the butter. Squeeze the roasted garlic cloves out of their skins into the skillet, then mash them gently with a fork to create a paste.
Pour the heavy cream into the skillet, stirring to combine with the roasted garlic. Bring to a gentle simmer.
Gradually whisk in the grated Parmesan cheese until melted and the sauce is smooth. If the sauce is too thick, add some reserved pasta water until you reach your desired consistency.
Season the sauce with salt and pepper to taste.
Add the cooked fettuccine to the skillet, tossing to coat the pasta evenly in the creamy sauce.
Serve immediately, garnished with fresh parsley for a pop of color.
Notes
For a lighter version, use half-and-half instead of heavy cream.