I lived in Lima for two years, so let me give you the real deal!
The fish: Use very fresh, firm white fish — sea bass (corvina) is the classic, but halibut or sole work well too. NEVER use frozen fish for real Peruvian ceviche — freshness is everything. Buy from a trusted fishmonger on the day you make it.
Leche de tigre (tiger’s milk): This is the marinade/sauce that makes Peruvian ceviche unique. Blend together: fresh lime juice, a small piece of fish, a bit of celery, half a garlic clove, fresh ginger, ají amarillo (Peruvian yellow chili), salt, and ice. Strain and use to marinate the fish.
Critical timing: Unlike Mexican ceviche, Peruvian ceviche marinates for only 3-5 minutes! The acid “cooks” only the outside — the center stays tender. Over-marinating makes it tough and dry.
Essential garnishes: Cancha (toasted Andean corn), sweet potato (camote), red onion slices soaked in cold water, and fresh cilantro. The combination of textures is key!
Where to find ají amarillo: Available as paste in Latin American grocery stores. Absolutely essential — nothing else gives that unique fruity heat.