• Heat 2 inches of oil in a large pan or iron skillet to 350°.
• While the oil is heating, whisk together the flour and the club soda. This will make a batter the consistency of pancake batter. Put 5-7 pieces of cod into the batter and when it is fully covered gently lower it into the oil. I use kitchen tongs for this job.
• Cook until the batter is golden brown on one side and then turn. Make sure the oil stays about 350°. When both sides are golden brown (about 6 minutes in total) transfer the fish to a rimmed baking sheet that has been fitted with a wire rack and put the fish into a 170° oven to keep warm. Fry fish in batches. Salt the fish after it comes out of the oil.
• While the fish is frying, put a corn tortilla directly on a burner over a medium flame, one at a time. Watch the tortillas carefully so they don't get totally burnt. Char the ends a little and turn. When the tortilla is gently charred on the ends, put them on a plate and set aside. Char 16 corn tortillas.
• If you do not have gas burners, wrap the tortillas in foil and put them in the warm oven with the fish.

To assemble

• Place 2 corn tortillas on top of each other on a plate. Lay down a bed of Napa cabbage and then place the fish on top of the cabbage. Place a slice or two of avocado and generously drizzle ranch dressing over the fish. Top the fish with the diced tomatoes, jalapaño rings, cilantro and a squeeze of fresh lime.
• Serve immediately.