The signature flavor of Aji de Gallina (“hen chili”) comes from aji amarillo peppers (Capsicum baccatum), which are prevalent in Peruvian and Bolivian cuisine. Fiercely spicy and naturally yellow, this pepper is eaten fresh (or in paste form) in Peru, like in today’s recipe, but they are often dried in Bolivia. Aji amarillo pastes can be found online or in your local Latin grocery, but can also be (somewhat) replicated using more conventional ingredients (more on that in the notes below).
This dish uses a unique mixture of New World and Old World ingredients. The aji amarillo paste and potatoes are native to the Americas, while the others — chicken, walnuts (to thicken the sauce), olives, milk, and parmesan cheese are all Old World staples introduced after the 15th century.