Combine the buttermilk, hot sauce and 2 tablespoons of the Essence in a medium mixing bowl, and stir to combine. Add the shrimp and marinate for up to 30 minutes in the refrigerator.

In a medium bowl, combine the masa harina, all-purpose flour, and remaining 2 tablespoons Essence, and stir to blend.

Heat the vegetable oil in a medium-size heavy pot or deep-fryier until the temperature reaches 360º F. Working in batches, remove the shrimp from the buttermilk marinade and transfer them to the masa harina mixture. Dredge to coat, shaking to remove any excess breading. Cook the shrimp in small batches in the 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.

To assemble: Spread the bottom halves of the bread with the melted butter. Generously spread the top halves of the bread with the mayonnaise. Divide the shrimp evenly among the bottom halves, followed by the lettuce and tomato. Place the top halves of the bread over the fillings and press lightly.

Serve immediately.