Add the egg yolks, pecorino romano, and black pepper into a bowl. Mix until it forms into a thick paste.
Bring a pot of water to a boil. Add the tteokbokki to the pot and boil for 3-4 minutes until they start to soften. Reserve 1 cup of water then drain the tteokbokki. Set aside.
Add the guanciale or beef bacon into a pan. Heat and cook over medium-low heat until the fat has rendered and the pieces are crisp and golden. Remove the guanciale pieces and set aside, leaving the fat in the pan.
Add the tteokbokki into the pan and coat them in the fat. Cook for a few minutes to slightly crisp them on the outside. In the meantime, begin whisking the egg mixture. While whisking, slowly stream in about a ½ cup of the hot pasta water into the egg mixture to temper it.
Remove the pan from heat and pour in the egg mixture over the pasta. Mix and toss quickly until a creamy sauce forms. Add ¼-½ cup more pasta water as needed to achieve the desired consistency. Mix in the crispy guanciale. Garnish with extra pecorino romano, black pepper, and chives.