How to Make It
In a small skillet, toast the white and black peppercorns over moderately high heat until fragrant, about 1 minute. Transfer them to a work surface and using the side of a heavy knife, coarsely crack the peppercorns; transfer to a large, deep bowl. Add the kosher salt and the brown sugar, then add the serrano chiles, garlic and one-third of the jalapeños. Stir in the warm water until the sugar and salt are dissolved. Add the pork and enough cold water to submerge the roast. Cover and refrigerate overnight.
Preheat the oven to 400°. Drain the pork and pat dry, then transfer to a roasting pan. Let the pork return to room temperature. Roast the pork for about 1 hour and 15 minutes, turning once; the pork is done when an instant-read thermometer inserted in the thickest part registers 165°. Let rest for 30 minutes before slicing thinly.
Meanwhile, in a medium bowl, combine the white vinegar, granulated sugar and table salt and stir until dissolved. Add the carrots and let stand until softened, about 30 minutes. Drain well.
Spread the cut sides of the rolls with mayonnaise and layer the sliced pĊté on the bottom halves. Top with roasted pork, cucumber, cilantro leaves, pickled carrots and the remaining sliced jalapeños. Sprinkle lightly with the soy sauce and close the sandwiches. Cut the ciabatta rolls in half or the baguettes in thirds and serve with hot sauce.