Whisk together the egg yolk and 1/4 C cream and set aside.
Melt the butter in a skillet, then add the garlic and cook on low until the garlic is fragrant.
Pour the remaining cream into the skillet, then while whisking bring to a simmer over medium-high heat. Slowly add the egg mixture, whisking continuously. Mix in 1 C of cheese to melt.
Mix in the remaining cheese, toss the pasta and options into the sauce, plate, garnish with parsley, and serve hot.