Step 1: Prepare Your Ingredients. Gather all your fresh ingredients. Dice your chosen white fish into 1/2 to 3/4-inch cubes. Slice the red onion very thinly, preferably using a mandoline, then rinse it in cold water to remove some of its harshness and pat dry. Finely chop your cilantro, and mince your aji limo or serrano pepper. Peel and dice the sweet potato and corn kernels if using.
Step 2: Make the ‘Leche de Tigre’ Base. In a medium non-reactive bowl (glass or ceramic), combine the fresh lime juice, aji amarillo paste, a small piece of fish (a scrap from your cubing), and a few cilantro stems (no leaves yet). Optionally, add a splash of fish broth or water for a milder flavor. Muddle gently to release flavors.
Step 3: Blend and Strain (Optional but Recommended). For the silkiest ‘leche de tigre,’ carefully transfer the mixture to a blender. Blend briefly until smooth, then immediately strain the mixture through a fine-mesh sieve into a clean bowl, pressing down on the solids to extract all the liquid. Discard the solids.
Step 4: Combine Fish and Aromatics. In a large bowl, gently combine your cubed fish, thinly sliced red onion, and minced aji limo/serrano pepper. Season lightly with salt and pepper.
Step 5: Marinate the Fish. Pour the ‘leche de tigre’ over the fish mixture. Ensure all the fish is submerged in the liquid. Gently stir to combine.
Step 6: Marination Time. Let the civeche marinate in the refrigerator. For firm fish like snapper or cod, 15-20 minutes is usually sufficient. For more delicate fish, 10-15 minutes might be enough. You’re looking for the fish to turn opaque around the edges and become firm. Do not over-marinate, or the fish will become rubbery.
Step 7: Finish and Serve. Just before serving, stir in the fresh chopped cilantro. Taste and adjust seasoning if necessary (more salt, a tiny bit more lime if needed). Serve your vibrant civeche immediately in chilled bowls or on a platter, garnished with sweet potato cubes, corn kernels, and extra cilantro sprigs. Enjoy!