Tip the flour, salt and baking powder into the bowl of a Chef XL Sense Stand Mixer. Start mixing with a Dough Hook and pour the oil and water into the bowl. Mix for a few minutes until the ingredients are well combined into a smooth dough.
Divide the dough into 16 balls (about 50g each). Flatten the balls into circles and set up a Lasagne Roller attachment onto the machine. Leave the flattened dough to rest for 30 minutes. Dust the dough and the roller with flour then roll out, turning 90oC after each pass through the roller, until the circles are just a few millimetres thick. Stack with baking paper between each tortilla.
Put a dry frying pan over a medium heat add the tortillas one at a time, cooking for about 1 minute each side. Stack the cooked tortillas with a clean tea towel over the top to keep them warm and pliable.
Quarter the tomatoes and cut out the seeds then chop the flesh into small dice. Peel and dice the onion as fine as possible. Deseed and chop the jalapeños (or leave the seeds in if you want it hot). Mix all three together with the coriander and a squeeze of lime. Season well with salt and pepper. Leave on the side for later. Mix up the sour cream, milk and mayo to create the white sauce. Season with salt and pepper.
Tip the flour into a mixing bowl with the baking powder and season with salt. Whisk in the water until you have a smooth but thick batter. Add the mustard, oregano and mayo then whisk together.
Heat the lard in a deep saucepan, only filling it halfway, until it reaches 180°C. Never leave it unattended. Slice the fish into goujons about the size of your thumb. Season with salt and pepper then dust in flour. Dunk in the batter to coat, allow excess to drip off, then lower into the lard to fry for 3-4 minutes, turning occasionally.
Drain the fried fish on kitchen paper to get rid of excess fat. Wash the lettuce and shred it finely using the Thin Slicing Disc of the Food Processor attachment. Warm the tortillas in a dry frying pan, oven or microwave. Pile the lettuce into the taco, followed by the fried fish. Top it off with plenty of the tomato salsa, a drizzle of the white sauce and a squeeze of lime. Serves 4