Crisp, golden fish and spicy, sour onion slaw (called salsa criolla) meet between slices of pillowy bread. Silverside are very tiny, thin fish, commonly known as “pejerrey” in Latin America; you’ll need about 24 pieces for this recipe because they are layered one on top of the other to make a thick sandwich. Since they’re not very easy to find, I often substitute it with grouper, swai, or flounder, for which I use half a filet per sandwich (you’ll need to slice the filets crosswise in half before coating them in the batter so they can fit into your potato rolls). You can find ají amarillo peppers in jars at most Latin American stores and online; if you can’t find whole peppers, then use ají amarillo paste instead. Make sure to let the bread rolls soak up a lot of the lemony juices of the sauce for the ultimate perfect bite.
Pro Tip: If not using cleaned silverfish (without heads, as is customary), you’ll need fish filets that are only ½-inch (or less) in thickness.
Pro tip: When turning battered food over while frying, use two forks instead of tongs so you don’t tear into the batter.
recipe 
yields
Makes 4 sandwiches
1½ cups very thinly sliced red onion
1 or 2 ají amarillo peppers, peeled, seeded, deveined, and very thinly sliced
4 tablespoons lime juice
1 teaspoon red wine vinegar
1 tablespoon extra-virgin olive oil
¼ cup packed cilantro, or more to taste
1½ teaspoons salt, divided, or more to taste
1 teaspoon freshly ground black pepper, divided
½ cup cornstarch
⅓ cup flour, divided
1 egg
¼ cup light beer
¼ cup sparkling or seltzer water
For the sandwiches:
1 pound silverside filets, (or other white fish filet; see headnote)
Avocado oil for frying
4 Peruvian potato buns
Deep-fry thermometer
Ingredients
For the onion salad:
For the batter:
Special equipment:
steps
- Make the onion salad: Place onion in a medium bowl and cover with cold water; let soak for 20 minutes and drain. Return to bowl; stir in ají, lime juice, vinegar, and olive oil. Season with half of the salt and pepper and let sit at room temperature for at least 30 minutes (or up to 2 hours, or refrigerate for up to 2 days). Just before serving, chop cilantro and stir it into sauce.
- Make the fish: Place cornstarch, 2 tablespoons of flour, egg, beer, and sparkling water in a medium bowl and whisk to combine until you have a batter; refrigerate for 20 minutes. Line a baking sheet with a metal cooling rack and set aside.
- Season fish with remaining salt and pepper. Place flour on a medium plate; dredge fish evenly on both sides in flour. Pour oil to ½-inch depth in a large, high-sided pan until it reaches 350 degrees (or until bubbles form around the handle of a wooden spoon inserted in the oil). Coat filets evenly with batter and carefully drop them into oil; cook until golden and crispy, 3 to 4 minutes per side. Remove filets and place on prepared cooling rack; allow fish to cool for 2 minutes (this will also ensure fish continues to cook through).
- Assemble the sandwiches: Slice potato rolls lengthwise in half. Place half a filet of fish on the bottom of the roll and top it with a generous amount of onion salad; cover with the other half of the bread and eat immediately.
