Preparing a great ceviche is a bit like making soup: tasting it along the way allows you build and balance the flavors without overpowering the delicate flavor of the fish. Serve it as cold as possible to keep it tasting fresh and clean. (Note: Recipe can easily be doubled or tripled.)
Umami Bomb: Dice onion and celery (pieces should be roughly the same size); set aside in a bowl. Slice the outer flesh from a habanero pepper and discard the stem and seeds. Dice the habanero, add to the bowl, and wash hands thoroughly (to avoid burning eyes and face). Peel and thinly slice garlic, and add to the bowl. Peel ginger, roughly chop, and add to the bowl. Add salt and stir to combine. Cover with plastic wrap and let rest at room temperature, 30 minutes.
Add the vegetables and their liquid to a blender. Purée until smooth, adding water a few tablespoons at a time as necessary to help blend. Pour the Umami Bomb into a bowl and set aside.
Ceviche and Leche de Tigre: Remove the skin and bloodline (dark flesh) from the fish and discard. Cut fish into ¾-inch cubes and place in a medium bowl. Add salt and stir to coat. Roll limes against the counter to release juice inside; slice 2 limes in half and lightly squeeze juice into bowl. Add fish stock and toss to coat. At this point, Chef Ramirez builds flavor by tasting and adjusting ingredients as he goes. First, add more lime juice, then ice cubes to both chill and dilute the Leche de Tigre. Add the Umami Bomb, ½-1 teaspoon at a time, followed by stirring, seasoning with salt, adding more ice cubes and lime juice, and tasting after each addition.
Slice the outer flesh from half a habanero pepper; thinly slice and add to ceviche, along with the sliced cilantro, mix and set aside. Fill a medium bowl with ice water. Thinly slice red onion on a mandoline and shock in ice water to both mellow and crisp up the onion, 30 seconds. Remove onions, pat dry on a paper towel, and add to the ceviche. Taste and adjust seasoning as necessary with more salt, lime juice, and Umami Bomb.
Assembly: Place ceviche into a shallow bowl, piling the fish and vegetables in the middle. Spoon the Leche de Tigre around the edges and serve immediately, chilled.