Bring a large pot of salted water to a rolling boil and cook the fettuccine pasta according to package instructions until al dente, which takes about 8 to 10 minutes.

Reserve 1/2 cup of the starchy pasta water right before draining, then drain the pasta and set it aside.

While the pasta cooks, melt the unsalted butter in a large skillet over medium-low heat. Add the roasted garlic paste, mashing it with a wooden spoon until it fully dissolves into the butter and becomes fragrant, about 2 minutes.

Pour the heavy cream into the skillet and bring the mixture to a gentle simmer, cooking for about 3 to 5 minutes until the cream has slightly thickened and easily coats the back of a spoon.

Reduce the heat to low and gradually whisk in the freshly grated Parmigiano-Reggiano cheese in small handfuls, letting each addition melt completely to ensure a smooth, velvety sauce.

Add the cooked fettuccine directly to the skillet and toss gently to coat the noodles, adding a splash of the reserved pasta water to loosen the sauce as needed before serving hot with a garnish of chopped parsley and black pepper.