Whisk the cream and egg yolk together in a large measuring cup until combined; set aside.

In a medium saucepan, melt the butter over medium-high. Add the garlic and sauté until fragrant and sizzling, about 2 minutes. Slowly pour the cream-yolk mixture into the garlic butter, reducing the heat immediately to medium and cook, stirring frequently, until mixture is hot to the touch but not boiling, about 5 minutes.

Whisk in the Parmesan little by little, and cook over medium, keep whisking, until cheese is melted. Continue to cook until the sauce becomes creamy and thickened, stirring frequently, about 3 to 5 minutes. Season to taste with pepper.