Cut each tilapia fillet in half lengthwise. Keep the shorter half of the fillet whole, but cut the longer half in half again widthwise. To a large bowl, add 1/4 cup cornstarch, 1/2 teaspoon baking powder and 2 teaspoons kosher salt, whisking to combine. Add the strips of tilapia, and toss until evenly coated. Transfer the fish to a wire rack set over a rimmed baking sheet, and refrigerate uncovered for 30 minutes or overnight. Meanwhile, make the crema.
When ready to fry, whisk together 1/2 cup cornstarch, 1/2 teaspoon baking powder, 1/2 cup flour and 2 teaspoons kosher salt in a large bowl. Add beer, and whisk until smooth. To test the consistency, dip a whisk into the batter, then pull up. If the batter runs off the whisk in a steady, thin stream, it's perfect. If it doesn't hold to the whisk, it's too thin. Whisk in a little flour and test again. If the batter runs off the whisk in a slower, thicker stream, it's too thick, whisk in a little beer and test again. Set batter aside for 15 minutes before using.
Meanwhile, fill a large cast-iron pot with enough oil to reach a depth of 2-inches, and preheat oil to 350°
Working in batches, dip the fillets in the beer batter one at a time, making sure the fish is fully coated. Let excess batter drip off, then carefully lower the fish in the oil. Don't overcrowd the batches as this will cause the temperature of the oil to drop quickly. Fry the fish until golden brown and cooked through (4 to 5 minutes).
Transfer to a wire rack and immediately sprinkle with salt.
To make the fish tacos, place 1 or 2 pieces of fried fish in a warm tortilla with shredded cabbage. Squeeze a lime over the fish and cabbage, then drizzle with chipotle crema. Finish with a few cilantro leaves. The fish tacos are best enjoyed immediately!
