Snow Roach Tacos

Procedure

1. Chill the batter. Whisk the all-purpose flour, ¼ cup of the cornstarch, baking powder, 1 teaspoon kosher salt, garlic powder and oregano in a medium metal bowl. Put the bowl and the unopened sparkling water in the freezer for 15 minutes while you make the crema and slaw and cut the fish. Cold is the whole trick.⏱ 15:00
2. Stir the crema. Stir the sour cream, mayonnaise, lime zest, 1 tablespoon lime juice and ¼ teaspoon kosher salt together. Add the water a teaspoon at a time until it drizzles from a spoon, then refrigerate.
3. Salt the slaw. Toss the green cabbage with 2 tablespoons lime juice and ½ teaspoon kosher salt and let it sit 10 minutes to soften slightly. Fold in the cilantro.⏱ 10:00
4. Prep the cod. Pat the cod fillets very dry and cut them into 4-by-1-inch (10 by 2.5 cm) strips. Season with ½ teaspoon kosher salt, then toss in the remaining ¼ cup cornstarch and shake off the excess; the dusting helps the batter grip.
5. Heat the oil. Pour the neutral oil into a heavy 4- to 5-quart (4 to 5 L) pot to a depth of 1½ inches (4 cm) and heat over medium-high to 365°F (185°C) on a clip-on thermometer. Set a wire rack over a sheet pan nearby. Stay with hot oil the entire time.
6. Warm the tortillas. While the oil heats, warm the blue corn tortillas in a dry skillet over medium-high heat, about 30 seconds per side, until soft and toasty. Stack them in a clean kitchen towel to stay warm.⏱ 0:30
7. Batter at the last second. Pour the ice-cold sparkling water into the frozen dry mix and whisk just until combined. Lumps are fine; overmixing wakes the gluten.
8. Fry. Dip a few strips of cod in the batter, let the excess drip off and lower them gently into the oil, away from you. Fry 4 or 5 at a time, turning once, until deep golden and the fish reaches 145°F (63°C) inside, 3 to 4 minutes. Drain on the rack, sprinkle with flaky sea salt and let the oil climb back to 365°F (185°C) before the next batch.⏱ 4:00
9. Bring the snowstorm. Fill each tortilla with slaw and a piece of fish, drizzle with crema and let the cotija cheese snow down over the top. Add pickled jalapeño slices, tuck in two chives so they arc up and back like antennae, and serve with the limes, cut into wedges.