1/2 c. plus 2 tbsp. fresh lime juice (divided use)
1 lb. small shrimp, unpeeled
1/2 medium white onion, chopped into 1/4-inch pieces
1/3 c. chopped fresh cilantro, plus several sprigs for garnish
1/2 c. ketchup
1 to 2 tbsp. vinegary Mexican bottled hot sauce
2 tbsp. extra-virgin olive oil (optional)
1 c. cucumber or jicama (or 1/2 c. of each), peeled and diced
1 small avocado, peeled, pitted and cubed
Salt
lime slices for garnish
Tostadas, tortilla chips or saltine crackers for serving

1. Cooking and Marinating the Shrimp: Bring 1 quart salted water to a boil and add 2 tablespoons lime juice. Scoop in the shrimp; cover and let water return to boil. Immediately remove from heat; set the lid askew and pour off all liquid. Replace the cover and let shrimp steam off the heat for 10 minutes. Spread out the shrimp in a large glass or stainless steel bowl to cool completely. Peel and devein the shrimp if you wish: One by one lay the shrimp on work surface, make a shallow incision down the back and scrape out the (usually) dark intestinal tract. Toss the shrimp with the remaining 1/2 lime juice, cover and refrigerate for about an hour.

2. The flavorings: In a small strainer, rinse onion under cold water, then shake off excess liquid. Add to shrimp bowl along with cilantro, ketchup, hot sauce, olive oil, cucumber and/or jcama and avocado. Taste and season with salt, usually about 1/2 teaspoon. Cover and refrigerate if not serving immediately.

3. Serving the ceviche: Spoon ceviche into sundae glasses, martini glasses, or small bowls; garnish with sprigs of cilantro and slices of lime. Serve with tostadas, tortilla chips or saltines to enjoy alongside.

Note: The ceviche is best made the day it is served. The flavorings can be added to the shrimp a few hours in advance.