Step 1In a heavy saucepan, combine the vinegar, water, salt and sugar over high heat until it comes to a boil. Remove from heat. Place the jalapeños in a large jar or medium glass bowl and pour over the liquid. Weight the jalapeños down so they stay submerged, and set aside until cool. Cover and refrigerate the submerged jalapeños for at least 12 hours to pickle. The jalapeños will keep for up to 2 weeks, covered and refrigerated.
Step 1In a large bowl, mix together the julienned cabbage and red onion, along with the strained pickled jalapeños.
Step 2In a small bowl, whisk together the pickling juice with the vinegar and olive oil to make a vinaigrette. Pour the vinaigrette over the slaw and season with a few pinches of salt to taste. Mix the slaw well and set aside for at least 10 minutes before using. This makes 6 to 8 cups slaw, possibly more than is needed for the rest of the recipe; the slaw will keep, covered and refrigerated, up to 3 days.
Step 1In the bowl of a food processor, combine the egg, yolk, mustard, lemon juice, garlic and kosher salt, blending until homogenous. With the processor running, slowly stream in the oil. As the oil is added, the mayonnaise will begin to emulsify and stiffen. Enough oil has added when the mayonnaise is thick and will form peaks. Stir in the malt vinegar by hand to form the aioli. This makes a generous cup aioli, which will keep, covered and refrigerated, up to 1 week.
Step 1Fill a 4-quart pot with frying oil to a depth of 3 to 4 inches. Heat the oil to maintain a temperature of 350 degrees.
Step 2Meanwhile, in a large bowl, whisk together 1 1/2 cups flour with the baking powder and kosher salt. Whisk in the beer unti the batter is smooth, then whisk in the Tabasco. Set aside.
Step 3Dredge the cod pieces in the remaining flour, then remove the cod and dip each piece into the batter. Carefully lower each piece into the oil and fry until golden and crispy, about 4 minutes (frying time will vary depending on the thickness of the pieces). Drain on a rack.
Step 4Assemble the sandwiches: Spread 1 to 2 tablespoons aioli on each half of the toasted rolls. Top the bottom half of each roll with a piece of fried fish, and top the fish with about 1 cup of loosely packed slaw. Top each sandwich with the remaining roll and serve immediately.