In a large pot, bring 1 quart salted water to a boil, add 2 tablespoons of the lime juice. Add the shrimp, cover and let the water return to the boil. Immediately remove from the heat. Put a large colander in the skin and pour the water/shrimp into the colander. Return the shrimp to the pot and replace the cover. Don’t put the pot back on the stove, leave it on the counter to allow the shrimp to steam (off the heat) for 10 minutes. Spread out the shrimp in a large glass bowl to cool completely. Peel and devein the shrimp. One by one lay the shrimp on your work surface, gently pull the shells off and discard. You can also save the shells to make shrimp stock. To devein: make a shallow incision down the back of each shrimp and, with a paring knife, scrape out the (usually) dark intestinal tract. Toss the shrimp with the remaining 1/2 lime juice, cover and refrigerate for about an hour.
In a small strainer, rinse the onion under cold water, then shake off the excess liquid. This is a neat trick that will take the bite out of the onion. Add the onion to the shrimp bowl along with the cilantro, ketchup, hot sauce, optional olive oil, cucumber and/or jícama and avocado. Taste and season with salt, usually about 1/2 teaspoon. Cover and refrigerate if not serving immediately.
When ready to serve, spoon the ceviche into sundae glasses, martini glasses, or small bowls. Garnish with sprigs of cilantro and slices of lime. Serve with tortilla chips.
TIP: The ceviche is best made the day it is served. The flavorings can be added to the shrimp a few hours in advance.
From Rick Baylis, Mexico One Plate at a Time