Bring a large pot of salted water to a rolling boil over high heat. Once boiling, add a pinch of salt.

Heat 2 tablespoons of extra virgin olive oil in a medium sauté pan over medium heat. Add the guanciale or smoked bacon, cooking until crispy and golden, about 5–7 minutes.

In a mixing bowl, whisk together 4 egg yolks, ½ cup Parmigiano Reggiano, 1–2 teaspoons crushed Calabrian chili, and 2 tablespoons of tomato paste until smooth. Gradually mix in about 2 tablespoons of the rendered fat from the guanciale.

Cook the spaghetti according to package instructions until al dente, reserving a cup of pasta water before draining.

Drain the pasta and immediately add it to the sauté pan with the guanciale. Off the heat, pour in the egg yolk mixture and a splash of reserved pasta water. Toss to combine.

Adjust the sauce consistency with reserved pasta water as needed. Stir in chopped Italian parsley. Serve garnished with chives and more cheese.