Make the sausage: Fill a medium pot ⅔ of the way with water. Bring to a boil over high heat, lower the heat, then cover to keep hot.

In the bowl of a food processor, add 3 tablespoons cold water, the fish sauce, canola oil, tapioca starch, baking powder, and sugar. Pulse several times to blend, then add the pork. Run the machine until the ingredients gather into a rough ball; turn off the processor, and let the mixture rest for 5 minutes to hydrate and season the meat.

Meanwhile, place two 12x16-inch pieces of aluminum foil side by side on a work surface, with the shorter sides closest to you. Center one banana leaf, smooth side up, on each, with the longer sides closest to you.

Grind the meat mixture in the processor, pausing to scrape down the sides as needed, until a relatively smooth, light-pink paste forms, about 2 minutes. Use a spatula to place half of the paste near the lower edge of one of the banana leaves. With damp hands, pat the paste into a 6½-inch-long log. Roll up the leaf to enclose the log, then roll the cylinder tightly in the foil like a burrito. Fold the ends closed and tap them gently against the table to set the shape. Tie with kitchen twine to keep secure during cooking. Repeat to form the other sausage.

Raise the heat to bring the water back up to a boil. Add the sausages and return to a low boil again, then cook for 25 minutes. (The foil might darken, and the sausages will swell and float.)

Remove and transfer the sausages to a plate. Refrigerate until completely chilled. (At this point, you can store the sausage for up to 1 week.)

Make the pâté: In a small pot, add the livers, stock, bay leaf, and peppercorns. Bring to a boil over medium-high heat, then adjust the heat to maintain a simmer. Cook until the livers are just cooked through (a little pinkness in the center is fine), 5–6 minutes.

Remove the livers and transfer to a food processor. Add the bread. Set a fine mesh strainer over a glass measuring cup and strain the liver-cooking liquid, discarding any solids or foam. Add ⅓ cup of the liquid to the livers, and reserve the rest.

In a medium skillet over medium-high heat, melt the butter. Once hot, add the shallot. Cook, stirring occasionally, until the shallots brown lightly, 4–6 minutes. Remove the pan from the heat, add the garlic and cognac, and stir until the hissing subsides.

Transfer the shallot mixture to the food processor. Add the five-spice powder, fish sauce, salt, and pepper. Purée, pausing to scrape down the sides with a spatula as needed. Keeping in mind that the pâté firms up as it rests, taste and add more cooking liquid if needed to soften, and salt and pepper as desired. Transfer the pâté to a jar and let rest for 10 minutes before using, or cover tightly and refrigerate for up to 1 week.

Make the sandwiches: Remove the sausage from the banana leaves and slice into ¼-inch-thick rounds. Spread the inside of each roll with 2 tablespoons of butter, 2 tablespoons of pâté, and ½ teaspoon of Maggi Seasoning or soy sauce. Top each with 10 thin slices (2 ounces) of the sausage, ¼ cup of pickles, 5 jalapeño slices, 6 cucumber slices, and ¼ cup of cilantro. Serve.