You're probably familiar with the Peruvian-style ceviche made with raw seafood cured with citrus juice and aromatics. The Colombian stuff is different. It's made with cooked shellfish and shrimp, langoustines, lobster, oysters, octopus, periwinkles, or whatever gets dragged up that days—dressed with lime juice, ketchup, mayonnaise, and perhaps some hot sauce and onions or cilantro. It comes served with saltines and it's damn delicious. Here's how to replicate it at home.