Baja Fish Tacos (Beer-Battered)

Steps

1. Make the salsa: seed the tomatoes and cut them into small dice, finely chop the white onion and jalapeño (remove the seeds for a milder salsa), and chop half the cilantro. Mix with the juice of half a lime and a pinch of salt, then refrigerate: the tomatoes will release a flavorful juice.
2. Make the crema: whisk the mayonnaise, sour cream, juice of 1 lime and a pinch of salt. Shred the cabbage as thinly as you can and toss with the juice of half a lime and a pinch of salt. Cut the last lime into wedges.
3. Cut the cod into strips about 4 inches by 1 inch (10 by 2.5 cm). Pat them very dry with paper towels, season with 1/2 teaspoon of the salt, and refrigerate.
4. Pour the oil into a large, deep saucepan or Dutch oven to a depth of 2 inches (5 cm), never more than half full. Heat over medium-high to 365°F (185°C) on a thermometer. Turn the oven on to 200°F (90°C) and set a wire rack on a baking sheet to keep the fish warm.
5. Right before frying, whisk together 140 g (1 cup plus 2 tablespoons) of the flour, the cornstarch, baking powder, garlic powder, oregano and 1 teaspoon of the salt. Pour in the ice-cold beer and whisk briefly; a few lumps are fine. The batter should be like drinkable yogurt and coat the back of a spoon. Put the remaining 30 g (1/4 cup) of flour on a plate.
6. Roll each strip in the plain flour, tap off the excess, dip it in the batter, and let it drip for 2 to 3 seconds. Lower it into the oil, laying it away from you. Fry 4 or 5 strips at a time for 3 to 4 minutes, turning halfway, until deep golden and very crisp; the bubbling quiets down when they are done, and the fish reaches 140°F (60°C) inside.
7. Drain the strips on the wire rack (not on paper towels, which steam the bottom soft), sprinkle with a pinch of salt right away, and keep them in the warm oven. Let the oil come back to 365°F (185°C) before each new batch.
8. Heat a dry skillet over high heat and warm the tortillas for 30 to 40 seconds per side, until pliable with a few brown spots. Stack them in a clean kitchen towel to keep them warm and soft.
9. Build the tacos: on each tortilla, a small handful of cabbage, a strip of fried fish, a spoonful of salsa, a drizzle of crema and a few cilantro leaves. Serve right away with lime wedges to squeeze at the table.