Callo de Lobina (Salt-Cured Sea Bass Tostadas)

Ingredients

• 1 pounds skinless striped sea bass fillets, cut into 2- x 1/3-inch pieces
• 4 teaspoons kosher salt, plus more to taste
• 4 cups ice cubes
• 1/3 cup fresh Key lime juice (from 6 limes)
• 2 tablespoons Worcestershire sauce
• 2 teaspoons soy sauce
• 1 teaspoon granulated sugar
• 1 teaspoon tomato paste
• 1/2 teaspoon hot sauce (such as Valentina)
• 1/2 teaspoon hot sauce (such as Valentina)
• 1/2 teaspoon freshly ground black pepper, plus more to taste
• 1/8 teaspoon ground dried pequin chile or cayenne pepper
• 2 large cucumbers (about 13 ounce each), peeled
• 1 (8-ounce) ripe avocado
• 1 small red onion, halved and thinly sliced (about 1 cup)
• 12 corn tostadas

Steps

1. Arrange sea bass pieces in a large glass or ceramic bowl; sprinkle all over with salt. Gently toss until fish is evenly coated. Add ice, and fold gently with a rubber spatula until salt dissolves and ice starts to melt and pool on bottom of bowl, about 5 minutes. Cover with plastic wrap, and refrigerate until fish is firm, about 1 hour, folding gently every 15 to 20 minutes.
2. Whisk together lime juice, Worcestershire sauce, soy sauce, sugar, tomato paste, hot sauce, black pepper, and pequin chile in a bowl until tomato paste dissolves and ingredients are fully combined. Set dressing aside.
3. Thinly slice 1 cucumber to equal 1 cup, and set aside. Dice remaining cucumber to equal 1 cup, and set aside. Cut avocado in half; reserve one half for another use. Cut remaining half lengthwise into 1/4-inch-thick slices, then cut crosswise into 1/4-inch-thick slices to equal about 1 cup. Set avocado aside.
4. Transfer fish to a colander; discard ice. Rinse fish under cold running water. Arrange fish in a single layer on a cutting board lined with paper towels to absorb excess water; pat fish dry.
5. Reserve 2 tablespoons dressing. Transfer fish to a clean glass or ceramic bowl. Add red onion, diced cucumber, and remaining dressing. Stir gently to combine. Season to taste with salt and black pepper.
6. To serve, scoop about 1/4 cup fish mixture onto each tostada. Top evenly with sliced cucumber, avocado pieces, and a drizzle of the reserved dressing. Serve tostadas immediately.