1. Combine the buttermilk, hot sauce, and 2 tablespoons of the Essence in a medium mixing bowl, and stir to combine. Add the oysters and marinate for up to 30 minutes, refrigerated.
2. In a separate medium bowl, combine the masa harina, all-purpose flour, and remaining 2 tablespoons Essence, and stir to blend.
3. Heat the vegetable oil in a medium-size heavy pot or deep-fryer until the temperature reaches 360°F. Working in batches, remove the oysters from the buttermilk marinade and transfer them to the masa harina mixture. Dredge to coat, shaking to remove any excess breading. Cook the oysters in small batches in the hot oil until golden brown and crispy, 2 to 3 minutes. Remove with a slotted spoon and transfer to paper towels to drain. Season with salt and pepper, and set aside.
4. To assemble: Spread the bottom halves of the bread with the melted butter. Generously spread the top halves of the bread with Jalapeño Mayonnaise. Divide the oysters evenly among the bottom halves, followed by the lettuce, tomato, avocado, and bacon. Place the top halves of the bread over the fillings and press lightly. Cut each sandwich in half and serve immediately.
If you don’t have buttermilk on hand, you can make your own by adding 1 tablespoon distilled white vinegar to 1 cup whole milk. Stir to blend and set aside until thickened and creamy, usually about 5 minutes; then use as needed.
Traditional New Orleans po’boy loaves are airy, long French breads. If you cannot find po’boy bread in your area, substitute any long Italian or French bread loaves that are not too dense. If the only bread you can find is very dense, consider pinching out the center doughy portions so that your po’boy is not overly bready.