Combine the masa harina, ¼ teaspoon of the salt, and 1¼ cups water in a medium bowl and stir until the mixture comes together. If the dough is dry and crumbly, add more water, 1 tablespoon at a time, until it comes together. Knead gently for 2 minutes. Divide the dough into 16 balls, each approximately 1½ inches in diameter. Cover the dough balls with a damp cloth to keep them moist. Line a tortilla press with two sheets of plastic wrap. Place a dough ball between the layers of plastic and press until the tortilla measures 4 inches in diameter, then carefully peel off the plastic wrap. (If you don’t have a tortilla press, you can use a heavy book and a little elbow grease to press them between sheets of plastic wrap.) Repeat with the remaining dough balls.

Put a large, dry skillet over medium-high heat. When it’s hot, cook the tortillas, one at a time, for about 50 seconds on each side. Cover the cooked tortillas with a dishtowel to keep them warm.

Make the sauce: Combine the mayonnaise, crema, milk, Sriracha, garlic, and the juice of ½ lime in a small bowl. Taste and adjust the seasoning. Cut the remaining 2½ limes into wedges.

Heat the oil to 350°F in a deep pot over medium-high heat. In a medium bowl, whisk together the flour, beer, and 1 teaspoon salt; the mixture should have the texture of pancake batter. When the oil is hot (if you don’t have a thermometer, you can test it by dropping in a bit of batter and seeing if it sizzles), dip the fish pieces in the batter and fry them in batches until golden brown, 2 to 3 minutes. Drain on paper towels and season with salt.

Arrange the tortillas on a serving plate and place one piece of fish on each. Top each taco with a large pinch of shredded cabbage, a drizzle of sauce, a slice of avocado, and a few cilantro leaves. Serve immediately with lime wedges and cold beer.